diff --git a/packages/compiler/src/ml_parser/lexer.ts b/packages/compiler/src/ml_parser/lexer.ts
index be34e8efa32..ce170b11961 100644
--- a/packages/compiler/src/ml_parser/lexer.ts
+++ b/packages/compiler/src/ml_parser/lexer.ts
@@ -89,6 +89,12 @@ export interface TokenizeOptions {
    * If true, do not convert CRLF to LF.
    */
   preserveLineEndings?: boolean;
+
+  // TODO(crisbeto): temporary option to limit access to the block syntax.
+  /**
+   * Whether the block syntax is enabled at the compiler level.
+   */
+  tokenizeBlocks?: boolean;
 }
 
 export function tokenize(
@@ -136,8 +142,8 @@ class _Tokenizer {
   private _expansionCaseStack: TokenType[] = [];
   private _inInterpolation: boolean = false;
   private readonly _preserveLineEndings: boolean;
-  private readonly _escapedString: boolean;
   private readonly _i18nNormalizeLineEndingsInICUs: boolean;
+  private readonly _tokenizeBlocks: boolean;
   tokens: Token[] = [];
   errors: TokenError[] = [];
   nonNormalizedIcuExpressions: Token[] = [];
@@ -159,8 +165,8 @@ class _Tokenizer {
     this._cursor = options.escapedString ? new EscapedCharacterCursor(_file, range) :
                                            new PlainCharacterCursor(_file, range);
     this._preserveLineEndings = options.preserveLineEndings || false;
-    this._escapedString = options.escapedString || false;
     this._i18nNormalizeLineEndingsInICUs = options.i18nNormalizeLineEndingsInICUs || false;
+    this._tokenizeBlocks = options.tokenizeBlocks || false;
     try {
       this._cursor.init();
     } catch (e) {
@@ -197,6 +203,12 @@ class _Tokenizer {
           } else {
             this._consumeTagOpen(start);
           }
+        } else if (this._tokenizeBlocks && this._attemptStr('{#')) {
+          this._consumeBlockGroupOpen(start);
+        } else if (this._tokenizeBlocks && this._attemptStr('{/')) {
+          this._consumeBlockGroupClose(start);
+        } else if (this._tokenizeBlocks && this._attemptStr('{:')) {
+          this._consumeBlock(start);
         } else if (!(this._tokenizeIcu && this._tokenizeExpansionForm())) {
           // In (possibly interpolated) text the end of the text is given by `isTextEnd()`, while
           // the premature end of an interpolation is given by the start of a new HTML element.
@@ -212,6 +224,72 @@ class _Tokenizer {
     this._endToken([]);
   }
 
+  private _consumeBlockGroupOpen(start: CharacterCursor) {
+    this._beginToken(TokenType.BLOCK_GROUP_OPEN_START, start);
+    const nameCursor = this._cursor.clone();
+    this._attemptCharCodeUntilFn(code => !isBlockNameChar(code));
+    this._endToken([this._cursor.getChars(nameCursor)]);
+    this._consumeBlockParameters();
+    this._beginToken(TokenType.BLOCK_GROUP_OPEN_END);
+    this._requireCharCode(chars.$RBRACE);
+    this._endToken([]);
+  }
+
+  private _consumeBlockGroupClose(start: CharacterCursor) {
+    this._beginToken(TokenType.BLOCK_GROUP_CLOSE, start);
+    const nameCursor = this._cursor.clone();
+    this._attemptCharCodeUntilFn(code => !isBlockNameChar(code));
+    const name = this._cursor.getChars(nameCursor);
+    this._requireCharCode(chars.$RBRACE);
+    this._endToken([name]);
+  }
+
+  private _consumeBlock(start: CharacterCursor) {
+    this._beginToken(TokenType.BLOCK_OPEN_START, start);
+    const nameCursor = this._cursor.clone();
+    this._attemptCharCodeUntilFn(code => !isBlockNameChar(code));
+    this._endToken([this._cursor.getChars(nameCursor)]);
+    this._consumeBlockParameters();
+    this._beginToken(TokenType.BLOCK_OPEN_END);
+    this._requireCharCode(chars.$RBRACE);
+    this._endToken([]);
+  }
+
+  private _consumeBlockParameters() {
+    // Trim the whitespace until the first parameter.
+    this._attemptCharCodeUntilFn(isBlockParameterChar);
+
+    while (this._cursor.peek() !== chars.$RBRACE && this._cursor.peek() !== chars.$EOF) {
+      this._beginToken(TokenType.BLOCK_PARAMETER);
+      const start = this._cursor.clone();
+      let inQuote: number|null = null;
+
+      // Consume the parameter until the next semicolon or brace.
+      // Note that we skip over semicolons/braces inside of strings.
+      while ((this._cursor.peek() !== chars.$SEMICOLON && this._cursor.peek() !== chars.$RBRACE &&
+              this._cursor.peek() !== chars.$EOF) ||
+             inQuote !== null) {
+        const char = this._cursor.peek();
+
+        // Skip to the next character if it was escaped.
+        if (char === chars.$BACKSLASH) {
+          this._cursor.advance();
+        } else if (char === inQuote) {
+          inQuote = null;
+        } else if (inQuote === null && chars.isQuote(char)) {
+          inQuote = char;
+        }
+
+        this._cursor.advance();
+      }
+
+      this._endToken([this._cursor.getChars(start)]);
+
+      // Skip to the next parameter.
+      this._attemptCharCodeUntilFn(isBlockParameterChar);
+    }
+  }
+
   /**
    * @returns whether an ICU token has been created
    * @internal
@@ -578,7 +656,6 @@ class _Tokenizer {
   }
 
   private _consumeAttributeValue() {
-    let value: string;
     if (this._cursor.peek() === chars.$SQ || this._cursor.peek() === chars.$DQ) {
       const quoteChar = this._cursor.peek();
       this._consumeQuote(quoteChar);
@@ -795,7 +872,7 @@ class _Tokenizer {
   }
 
   private _isTextEnd(): boolean {
-    if (this._isTagStart() || this._cursor.peek() === chars.$EOF) {
+    if (this._isTagStart() || this._isBlockStart() || this._cursor.peek() === chars.$EOF) {
       return true;
     }
 
@@ -833,6 +910,26 @@ class _Tokenizer {
     return false;
   }
 
+  private _isBlockStart(): boolean {
+    if (this._tokenizeBlocks && this._cursor.peek() === chars.$LBRACE) {
+      const tmp = this._cursor.clone();
+
+      // Check that the cursor is on a `{#`, `{/` or `{:`.
+      tmp.advance();
+      const next = tmp.peek();
+      if (next !== chars.$BANG && next !== chars.$SLASH && next !== chars.$COLON) {
+        return false;
+      }
+
+      // If it is, also verify that the next character is a valid block identifier.
+      tmp.advance();
+      if (isBlockNameChar(tmp.peek())) {
+        return true;
+      }
+    }
+    return false;
+  }
+
   private _readUntil(char: number): string {
     const start = this._cursor.clone();
     this._attemptUntilChar(char);
@@ -900,6 +997,14 @@ function toUpperCaseCharCode(code: number): number {
   return code >= chars.$a && code <= chars.$z ? code - chars.$a + chars.$A : code;
 }
 
+function isBlockNameChar(code: number): boolean {
+  return chars.isAsciiLetter(code) || chars.isDigit(code) || code === chars.$_;
+}
+
+function isBlockParameterChar(code: number): boolean {
+  return code !== chars.$SEMICOLON && isNotWhitespace(code);
+}
+
 function mergeTextTokens(srcTokens: Token[]): Token[] {
   const dstTokens: Token[] = [];
   let lastDstToken: Token|undefined = undefined;
diff --git a/packages/compiler/src/ml_parser/tokens.ts b/packages/compiler/src/ml_parser/tokens.ts
index 643dc250031..43c9fb9ae3e 100644
--- a/packages/compiler/src/ml_parser/tokens.ts
+++ b/packages/compiler/src/ml_parser/tokens.ts
@@ -33,7 +33,13 @@ export const enum TokenType {
   EXPANSION_CASE_EXP_START,
   EXPANSION_CASE_EXP_END,
   EXPANSION_FORM_END,
-  EOF
+  EOF,
+  BLOCK_GROUP_OPEN_START,
+  BLOCK_GROUP_OPEN_END,
+  BLOCK_GROUP_CLOSE,
+  BLOCK_PARAMETER,
+  BLOCK_OPEN_START,
+  BLOCK_OPEN_END,
 }
 
 export type Token = TagOpenStartToken|TagOpenEndToken|TagOpenEndVoidToken|TagCloseToken|
@@ -41,7 +47,8 @@ export type Token = TagOpenStartToken|TagOpenEndToken|TagOpenEndVoidToken|TagClo
     CommentEndToken|CdataStartToken|CdataEndToken|AttributeNameToken|AttributeQuoteToken|
     AttributeValueTextToken|AttributeValueInterpolationToken|DocTypeToken|ExpansionFormStartToken|
     ExpansionCaseValueToken|ExpansionCaseExpressionStartToken|ExpansionCaseExpressionEndToken|
-    ExpansionFormEndToken|EndOfFileToken;
+    ExpansionFormEndToken|EndOfFileToken|BlockGroupOpenStartToken|BlockGroupOpenEndToken|
+    BlockGroupCloseToken|BlockParameterToken|BlockOpenStartToken|BlockOpenEndToken;
 
 export type InterpolatedTextToken = TextToken|InterpolationToken|EncodedEntityToken;
 
@@ -170,3 +177,33 @@ export interface EndOfFileToken extends TokenBase {
   type: TokenType.EOF;
   parts: [];
 }
+
+export interface BlockGroupOpenStartToken extends TokenBase {
+  type: TokenType.BLOCK_GROUP_OPEN_START;
+  parts: [name: string];
+}
+
+export interface BlockGroupOpenEndToken extends TokenBase {
+  type: TokenType.BLOCK_GROUP_OPEN_END;
+  parts: [];
+}
+
+export interface BlockGroupCloseToken extends TokenBase {
+  type: TokenType.BLOCK_GROUP_CLOSE;
+  parts: [name: string];
+}
+
+export interface BlockParameterToken extends TokenBase {
+  type: TokenType.BLOCK_PARAMETER;
+  parts: [expression: string];
+}
+
+export interface BlockOpenStartToken extends TokenBase {
+  type: TokenType.BLOCK_OPEN_START;
+  parts: [name: string];
+}
+
+export interface BlockOpenEndToken extends TokenBase {
+  type: TokenType.BLOCK_OPEN_END;
+  parts: [];
+}
diff --git a/packages/compiler/test/ml_parser/lexer_spec.ts b/packages/compiler/test/ml_parser/lexer_spec.ts
index c1b73cc19d5..ea5a1a3c548 100644
--- a/packages/compiler/test/ml_parser/lexer_spec.ts
+++ b/packages/compiler/test/ml_parser/lexer_spec.ts
@@ -1814,6 +1814,222 @@ import {ParseLocation, ParseSourceFile, ParseSourceSpan} from '../../src/parse_u
         ]);
       });
     });
+
+    describe('blocks', () => {
+      // TODO(crisbeto): temporary utility while blocks are disabled by default.
+      function tokenizeBlock(input: string, options: TokenizeOptions = {}): any[] {
+        return tokenizeAndHumanizeParts(input, {tokenizeBlocks: true, ...options});
+      }
+
+      it('should parse a block group', () => {
+        expect(tokenizeBlock('{#foo}hello{/foo}')).toEqual([
+          [TokenType.BLOCK_GROUP_OPEN_START, 'foo'],
+          [TokenType.BLOCK_GROUP_OPEN_END],
+          [TokenType.TEXT, 'hello'],
+          [TokenType.BLOCK_GROUP_CLOSE, 'foo'],
+          [TokenType.EOF],
+        ]);
+      });
+
+      it('should parse a block group with parameters', () => {
+        expect(tokenizeBlock('{#for item of items; track item.id}hello{/for}')).toEqual([
+          [TokenType.BLOCK_GROUP_OPEN_START, 'for'],
+          [TokenType.BLOCK_PARAMETER, 'item of items'],
+          [TokenType.BLOCK_PARAMETER, 'track item.id'],
+          [TokenType.BLOCK_GROUP_OPEN_END],
+          [TokenType.TEXT, 'hello'],
+          [TokenType.BLOCK_GROUP_CLOSE, 'for'],
+          [TokenType.EOF],
+        ]);
+      });
+
+      it('should parse a block group with a trailing semicolon after the parameters', () => {
+        expect(tokenizeBlock('{#for item of items;}hello{/for}')).toEqual([
+          [TokenType.BLOCK_GROUP_OPEN_START, 'for'],
+          [TokenType.BLOCK_PARAMETER, 'item of items'],
+          [TokenType.BLOCK_GROUP_OPEN_END],
+          [TokenType.TEXT, 'hello'],
+          [TokenType.BLOCK_GROUP_CLOSE, 'for'],
+          [TokenType.EOF],
+        ]);
+      });
+
+      it('should parse a block group with multiple trailing semicolons', () => {
+        expect(tokenizeBlock('{#for item of items;;;;;}hello{/for}')).toEqual([
+          [TokenType.BLOCK_GROUP_OPEN_START, 'for'],
+          [TokenType.BLOCK_PARAMETER, 'item of items'],
+          [TokenType.BLOCK_GROUP_OPEN_END],
+          [TokenType.TEXT, 'hello'],
+          [TokenType.BLOCK_GROUP_CLOSE, 'for'],
+          [TokenType.EOF],
+        ]);
+      });
+
+      it('should parse a block group with trailing whitespace', () => {
+        expect(tokenizeBlock('{#foo                        }hello{/foo}')).toEqual([
+          [TokenType.BLOCK_GROUP_OPEN_START, 'foo'],
+          [TokenType.BLOCK_GROUP_OPEN_END],
+          [TokenType.TEXT, 'hello'],
+          [TokenType.BLOCK_GROUP_CLOSE, 'foo'],
+          [TokenType.EOF],
+        ]);
+      });
+
+      it('should parse a block group with no trailing semicolon', () => {
+        expect(tokenizeBlock('{#for item of items}hello{/for}')).toEqual([
+          [TokenType.BLOCK_GROUP_OPEN_START, 'for'],
+          [TokenType.BLOCK_PARAMETER, 'item of items'],
+          [TokenType.BLOCK_GROUP_OPEN_END],
+          [TokenType.TEXT, 'hello'],
+          [TokenType.BLOCK_GROUP_CLOSE, 'for'],
+          [TokenType.EOF],
+        ]);
+      });
+
+      it('should handle semicolons and braces used in a block group parameter', () => {
+        expect(tokenizeBlock(`{#foo a === ";"; b === '}'}hello{/foo}`)).toEqual([
+          [TokenType.BLOCK_GROUP_OPEN_START, 'foo'],
+          [TokenType.BLOCK_PARAMETER, `a === ";"`],
+          [TokenType.BLOCK_PARAMETER, `b === '}'`],
+          [TokenType.BLOCK_GROUP_OPEN_END],
+          [TokenType.TEXT, 'hello'],
+          [TokenType.BLOCK_GROUP_CLOSE, 'foo'],
+          [TokenType.EOF],
+        ]);
+      });
+
+      it('should throw for invalid quotes in a parameter', () => {
+        const options = {tokenizeBlocks: true};
+
+        expect(tokenizeAndHumanizeErrors(`{#foo a === "}hello{/foo}`, options)).toEqual([
+          [TokenType.BLOCK_PARAMETER, 'Unexpected character "EOF"', '0:25']
+        ]);
+
+        expect(tokenizeAndHumanizeErrors(`{#foo a === "hi'}hello{/foo}`, options)).toEqual([
+          [TokenType.BLOCK_PARAMETER, 'Unexpected character "EOF"', '0:28']
+        ]);
+      });
+
+      it('should handle a semicolon used in a nested string inside a block group parameter', () => {
+        expect(tokenizeBlock(`{#if condition === "';'"}hello{/if}`)).toEqual([
+          [TokenType.BLOCK_GROUP_OPEN_START, 'if'],
+          [TokenType.BLOCK_PARAMETER, `condition === "';'"`],
+          [TokenType.BLOCK_GROUP_OPEN_END],
+          [TokenType.TEXT, 'hello'],
+          [TokenType.BLOCK_GROUP_CLOSE, 'if'],
+          [TokenType.EOF],
+        ]);
+      });
+
+      it('should handle a semicolon next to an escaped quote used in a block group parameter',
+         () => {
+           expect(tokenizeBlock('{#if condition === "\\";"}hello{/if}')).toEqual([
+             [TokenType.BLOCK_GROUP_OPEN_START, 'if'],
+             [TokenType.BLOCK_PARAMETER, 'condition === "\\";"'],
+             [TokenType.BLOCK_GROUP_OPEN_END],
+             [TokenType.TEXT, 'hello'],
+             [TokenType.BLOCK_GROUP_CLOSE, 'if'],
+             [TokenType.EOF],
+           ]);
+         });
+
+      it('should parse mixed text and html content in a block group', () => {
+        expect(tokenizeBlock('{#if a === 1}foo <b>bar</b> baz{/if}')).toEqual([
+          [TokenType.BLOCK_GROUP_OPEN_START, 'if'],
+          [TokenType.BLOCK_PARAMETER, 'a === 1'],
+          [TokenType.BLOCK_GROUP_OPEN_END],
+          [TokenType.TEXT, 'foo '],
+          [TokenType.TAG_OPEN_START, '', 'b'],
+          [TokenType.TAG_OPEN_END],
+          [TokenType.TEXT, 'bar'],
+          [TokenType.TAG_CLOSE, '', 'b'],
+          [TokenType.TEXT, ' baz'],
+          [TokenType.BLOCK_GROUP_CLOSE, 'if'],
+          [TokenType.EOF],
+        ]);
+      });
+
+      it('should parse a block group with blocks', () => {
+        expect(tokenizeBlock(
+                   '{#if expr}' +
+                   'foo' +
+                   '{:else if otherExpr === 1}' +
+                   '<some-comp/>' +
+                   '{:else}' +
+                   'bar' +
+                   '{/if}'))
+            .toEqual([
+              [TokenType.BLOCK_GROUP_OPEN_START, 'if'],
+              [TokenType.BLOCK_PARAMETER, 'expr'],
+              [TokenType.BLOCK_GROUP_OPEN_END],
+              [TokenType.TEXT, 'foo'],
+              [TokenType.BLOCK_OPEN_START, 'else'],
+              [TokenType.BLOCK_PARAMETER, 'if otherExpr === 1'],
+              [TokenType.BLOCK_OPEN_END],
+              [TokenType.TAG_OPEN_START, '', 'some-comp'],
+              [TokenType.TAG_OPEN_END_VOID],
+              [TokenType.BLOCK_OPEN_START, 'else'],
+              [TokenType.BLOCK_OPEN_END],
+              [TokenType.TEXT, 'bar'],
+              [TokenType.BLOCK_GROUP_CLOSE, 'if'],
+              [TokenType.EOF],
+            ]);
+      });
+
+      it('should parse nested block groups', () => {
+        expect(tokenizeBlock(
+                   '{#if a}' +
+                   'hello a' +
+                   '{:else}' +
+                   '{#if b}' +
+                   'hello b' +
+                   '{:else}' +
+                   '{#if c}hello c{/if}' +
+                   '{/if}' +
+                   '{/if}'))
+            .toEqual([
+              [TokenType.BLOCK_GROUP_OPEN_START, 'if'], [TokenType.BLOCK_PARAMETER, 'a'],
+              [TokenType.BLOCK_GROUP_OPEN_END],         [TokenType.TEXT, 'hello a'],
+              [TokenType.BLOCK_OPEN_START, 'else'],     [TokenType.BLOCK_OPEN_END],
+              [TokenType.BLOCK_GROUP_OPEN_START, 'if'], [TokenType.BLOCK_PARAMETER, 'b'],
+              [TokenType.BLOCK_GROUP_OPEN_END],         [TokenType.TEXT, 'hello b'],
+              [TokenType.BLOCK_OPEN_START, 'else'],     [TokenType.BLOCK_OPEN_END],
+              [TokenType.BLOCK_GROUP_OPEN_START, 'if'], [TokenType.BLOCK_PARAMETER, 'c'],
+              [TokenType.BLOCK_GROUP_OPEN_END],         [TokenType.TEXT, 'hello c'],
+              [TokenType.BLOCK_GROUP_CLOSE, 'if'],      [TokenType.BLOCK_GROUP_CLOSE, 'if'],
+              [TokenType.BLOCK_GROUP_CLOSE, 'if'],      [TokenType.EOF],
+            ]);
+      });
+
+      it('should parse a block group containing an expansion', () => {
+        const result = tokenizeBlock(
+            '{#foo}{one.two, three, =4 {four} =5 {five} foo {bar} }{/foo}',
+            {tokenizeExpansionForms: true});
+
+        expect(result).toEqual([
+          [TokenType.BLOCK_GROUP_OPEN_START, 'foo'],
+          [TokenType.BLOCK_GROUP_OPEN_END],
+          [TokenType.EXPANSION_FORM_START],
+          [TokenType.RAW_TEXT, 'one.two'],
+          [TokenType.RAW_TEXT, 'three'],
+          [TokenType.EXPANSION_CASE_VALUE, '=4'],
+          [TokenType.EXPANSION_CASE_EXP_START],
+          [TokenType.TEXT, 'four'],
+          [TokenType.EXPANSION_CASE_EXP_END],
+          [TokenType.EXPANSION_CASE_VALUE, '=5'],
+          [TokenType.EXPANSION_CASE_EXP_START],
+          [TokenType.TEXT, 'five'],
+          [TokenType.EXPANSION_CASE_EXP_END],
+          [TokenType.EXPANSION_CASE_VALUE, 'foo'],
+          [TokenType.EXPANSION_CASE_EXP_START],
+          [TokenType.TEXT, 'bar'],
+          [TokenType.EXPANSION_CASE_EXP_END],
+          [TokenType.EXPANSION_FORM_END],
+          [TokenType.BLOCK_GROUP_CLOSE, 'foo'],
+          [TokenType.EOF],
+        ]);
+      });
+    });
   });
 }