diff --git a/emacs/Makefile.local b/emacs/Makefile.local
index 456700ac..a910affa 100644
--- a/emacs/Makefile.local
+++ b/emacs/Makefile.local
@@ -3,6 +3,7 @@
 dir := emacs
 emacs_sources := \
 	$(dir)/notmuch-lib.el \
+	$(dir)/notmuch-parser.el \
 	$(dir)/notmuch.el \
 	$(dir)/notmuch-query.el \
 	$(dir)/notmuch-show.el \
diff --git a/emacs/notmuch-parser.el b/emacs/notmuch-parser.el
new file mode 100644
index 00000000..d59c0e1c
--- /dev/null
+++ b/emacs/notmuch-parser.el
@@ -0,0 +1,207 @@
+;; notmuch-parser.el --- streaming S-expression parser
+;;
+;; Copyright © Austin Clements
+;;
+;; This file is part of Notmuch.
+;;
+;; Notmuch is free software: you can redistribute it and/or modify it
+;; under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+;;
+;; Notmuch is distributed in the hope that it will be useful, but
+;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;; General Public License for more details.
+;;
+;; You should have received a copy of the GNU General Public License
+;; along with Notmuch.  If not, see <http://www.gnu.org/licenses/>.
+;;
+;; Authors: Austin Clements <aclements@csail.mit.edu>
+
+(require 'cl)
+
+(defun notmuch-sexp-create-parser ()
+  "Return a new streaming S-expression parser.
+
+This parser is designed to incrementally read an S-expression
+whose structure is known to the caller.  Like a typical
+S-expression parsing interface, it provides a function to read a
+complete S-expression from the input.  However, it extends this
+with an additional function that requires the next value in the
+input to be a list and descends into it, allowing its elements to
+be read one at a time or further descended into.  Both functions
+can return 'retry to indicate that not enough input is available.
+
+The parser always consumes input from point in the current
+buffer.  Hence, the caller is allowed to delete any data before
+point and may resynchronize after an error by moving point."
+
+  (vector 'notmuch-sexp-parser
+	  ;; List depth
+	  0
+	  ;; Partial parse position marker
+	  nil
+	  ;; Partial parse state
+	  nil))
+
+(defmacro notmuch-sexp--depth (sp)         `(aref ,sp 1))
+(defmacro notmuch-sexp--partial-pos (sp)   `(aref ,sp 2))
+(defmacro notmuch-sexp--partial-state (sp) `(aref ,sp 3))
+
+(defun notmuch-sexp-read (sp)
+  "Consume and return the value at point in the current buffer.
+
+Returns 'retry if there is insufficient input to parse a complete
+value (though it may still move point over whitespace).  If the
+parser is currently inside a list and the next token ends the
+list, this moves point just past the terminator and returns 'end.
+Otherwise, this moves point to just past the end of the value and
+returns the value."
+
+  (skip-chars-forward " \n\r\t")
+  (cond ((eobp) 'retry)
+	((= (char-after) ?\))
+	 ;; We've reached the end of a list
+	 (if (= (notmuch-sexp--depth sp) 0)
+	     ;; .. but we weren't in a list.  Let read signal the
+	     ;; error to be consistent with all other code paths.
+	     (read (current-buffer))
+	   ;; Go up a level and return an end token
+	   (decf (notmuch-sexp--depth sp))
+	   (forward-char)
+	   'end))
+	((= (char-after) ?\()
+	 ;; We're at the beginning of a list.  If we haven't started
+	 ;; a partial parse yet, attempt to read the list in its
+	 ;; entirety.  If this fails, or we've started a partial
+	 ;; parse, extend the partial parse to figure out when we
+	 ;; have a complete list.
+	 (catch 'return
+	   (when (null (notmuch-sexp--partial-state sp))
+	     (let ((start (point)))
+	       (condition-case nil
+		   (throw 'return (read (current-buffer)))
+		 (end-of-file (goto-char start)))))
+	   ;; Extend the partial parse
+	   (let (is-complete)
+	     (save-excursion
+	       (let* ((new-state (parse-partial-sexp
+				  (or (notmuch-sexp--partial-pos sp) (point))
+				  (point-max) 0 nil
+				  (notmuch-sexp--partial-state sp)))
+		      ;; A complete value is available if we've
+		      ;; reached depth 0.
+		      (depth (first new-state)))
+		 (assert (>= depth 0))
+		 (if (= depth 0)
+		     ;; Reset partial parse state
+		     (setf (notmuch-sexp--partial-state sp) nil
+			   (notmuch-sexp--partial-pos sp) nil
+			   is-complete t)
+		   ;; Update partial parse state
+		   (setf (notmuch-sexp--partial-state sp) new-state
+			 (notmuch-sexp--partial-pos sp) (point-marker)))))
+	     (if is-complete
+		 (read (current-buffer))
+	       'retry))))
+	(t
+	 ;; Attempt to read a non-compound value
+	 (let ((start (point)))
+	   (condition-case nil
+	       (let ((val (read (current-buffer))))
+		 ;; We got what looks like a complete read, but if
+		 ;; we reached the end of the buffer in the process,
+		 ;; we may not actually have all of the input we
+		 ;; need (unless it's a string, which is delimited).
+		 (if (or (stringp val) (not (eobp)))
+		     val
+		   ;; We can't be sure the input was complete
+		   (goto-char start)
+		   'retry))
+	     (end-of-file
+	      (goto-char start)
+	      'retry))))))
+
+(defun notmuch-sexp-begin-list (sp)
+  "Parse the beginning of a list value and enter the list.
+
+Returns 'retry if there is insufficient input to parse the
+beginning of the list.  If this is able to parse the beginning of
+a list, it moves point past the token that opens the list and
+returns t.  Later calls to `notmuch-sexp-read' will return the
+elements inside the list.  If the input in buffer is not the
+beginning of a list, throw invalid-read-syntax."
+
+  (skip-chars-forward " \n\r\t")
+  (cond ((eobp) 'retry)
+	((= (char-after) ?\()
+	 (forward-char)
+	 (incf (notmuch-sexp--depth sp))
+	 t)
+	(t
+	 ;; Skip over the bad character like `read' does
+	 (forward-char)
+	 (signal 'invalid-read-syntax (list (string (char-before)))))))
+
+(defun notmuch-sexp-eof (sp)
+  "Signal an error if there is more data in SP's buffer.
+
+Moves point to the beginning of any trailing data or to the end
+of the buffer if there is only trailing whitespace."
+
+  (skip-chars-forward " \n\r\t")
+  (unless (eobp)
+    (error "Trailing garbage following expression")))
+
+(defvar notmuch-sexp--parser nil
+  "The buffer-local notmuch-sexp-parser instance.
+
+Used by `notmuch-sexp-parse-partial-list'.")
+
+(defvar notmuch-sexp--state nil
+  "The buffer-local `notmuch-sexp-parse-partial-list' state.")
+
+(defun notmuch-sexp-parse-partial-list (result-function result-buffer)
+  "Incrementally parse an S-expression list from the current buffer.
+
+This function consumes an S-expression list from the current
+buffer, applying RESULT-FUNCTION in RESULT-BUFFER to each
+complete value in the list.  It operates incrementally and should
+be called whenever the input buffer has been extended with
+additional data.  The caller just needs to ensure it does not
+move point in the input buffer."
+
+  ;; Set up the initial state
+  (unless (local-variable-p 'notmuch-sexp--parser)
+    (set (make-local-variable 'notmuch-sexp--parser)
+	 (notmuch-sexp-create-parser))
+    (set (make-local-variable 'notmuch-sexp--state) 'begin))
+  (let (done)
+    (while (not done)
+      (case notmuch-sexp--state
+	(begin
+	 ;; Enter the list
+	 (if (eq (notmuch-sexp-begin-list notmuch-sexp--parser) 'retry)
+	     (setq done t)
+	   (setq notmuch-sexp--state 'result)))
+	(result
+	 ;; Parse a result
+	 (let ((result (notmuch-sexp-read notmuch-sexp--parser)))
+	   (case result
+	     (retry (setq done t))
+	     (end   (setq notmuch-sexp--state 'end))
+	     (t     (with-current-buffer result-buffer
+		      (funcall result-function result))))))
+	(end
+	 ;; Any trailing data is unexpected
+	 (notmuch-sexp-eof notmuch-sexp--parser)
+	 (setq done t)))))
+  ;; Clear out what we've parsed
+  (delete-region (point-min) (point)))
+
+(provide 'notmuch-parser)
+
+;; Local Variables:
+;; byte-compile-warnings: (not cl-functions)
+;; End: