diff --git a/Development Ideas.ipynb b/Development Ideas.ipynb
index 7139fa3..c991418 100644
--- a/Development Ideas.ipynb	
+++ b/Development Ideas.ipynb	
@@ -3,7 +3,10 @@
   {
    "cell_type": "markdown",
    "metadata": {
-    "collapsed": true
+    "collapsed": true,
+    "tags": [
+     "worksheet-0"
+    ]
    },
    "source": [
     "# Adding Imenu Support"
@@ -12,7 +15,10 @@
   {
    "cell_type": "markdown",
    "metadata": {
-    "collapsed": true
+    "collapsed": true,
+    "tags": [
+     "worksheet-0"
+    ]
    },
    "source": [
     "## Subheader"
@@ -21,7 +27,10 @@
   {
    "cell_type": "markdown",
    "metadata": {
-    "collapsed": true
+    "collapsed": true,
+    "tags": [
+     "worksheet-0"
+    ]
    },
    "source": [
     "Seems to be a couple ways of doing this:\n",
@@ -35,7 +44,10 @@
    "cell_type": "code",
    "execution_count": 2,
    "metadata": {
-    "collapsed": false
+    "collapsed": false,
+    "tags": [
+     "worksheet-0"
+    ]
    },
    "outputs": [],
    "source": [
@@ -55,7 +67,10 @@
   {
    "cell_type": "markdown",
    "metadata": {
-    "collapsed": true
+    "collapsed": true,
+    "tags": [
+     "worksheet-0"
+    ]
    },
    "source": [
     "# Another Header"
@@ -63,9 +78,12 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 3,
+   "execution_count": 4,
    "metadata": {
-    "collapsed": false
+    "collapsed": false,
+    "tags": [
+     "worksheet-0"
+    ]
    },
    "outputs": [
     {
@@ -75,7 +93,7 @@
      "traceback": [
       "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
       "\u001b[1;31mZeroDivisionError\u001b[0m                         Traceback (most recent call last)",
-      "\u001b[1;32m<ipython-input-3-05c9758a9c21>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[1;36m1\u001b[0m\u001b[1;33m/\u001b[0m\u001b[1;36m0\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
+      "\u001b[1;32m<ipython-input-4-05c9758a9c21>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[1;36m1\u001b[0m\u001b[1;33m/\u001b[0m\u001b[1;36m0\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
       "\u001b[1;31mZeroDivisionError\u001b[0m: division by zero"
      ]
     }
@@ -84,11 +102,68 @@
     "1/0"
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "metadata": {
+    "collapsed": false,
+    "tags": [
+     "worksheet-0"
+    ]
+   },
+   "outputs": [],
+   "source": [
+    "import inspect"
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
-    "collapsed": false
+    "collapsed": false,
+    "tags": [
+     "worksheet-0"
+    ]
+   },
+   "outputs": [],
+   "source": []
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": false,
+    "tags": [
+     "worksheet-1"
+    ]
+   },
+   "outputs": [],
+   "source": [
+    "1+1"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": false,
+    "tags": [
+     "worksheet-1"
+    ]
+   },
+   "outputs": [],
+   "source": [
+    "inspect"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": false,
+    "tags": [
+     "worksheet-1"
+    ]
    },
    "outputs": [],
    "source": []
diff --git a/Enhancements.org b/Enhancements.org
index 0cb30a2..1fad9e5 100644
--- a/Enhancements.org
+++ b/Enhancements.org
@@ -3,6 +3,13 @@
 * Overview
 * Design
 ** Notebook Buffer
+
+Notebook information is stored as a [[file:lisp/ein-notebook.el::ein:$notebook][struct]]. Always associated with a buffer,
+[[file:lisp/ein-notebook.el::ein:notebook-buffer][ein:notebook-buffer]] is used to find buffer associated with a notebook.
+
+Notebook does not hold cells, that is delegated to instances of the [[file:lisp/ein-worksheet.el::ein:worksheet][worksheet]]
+class. Instances are stored as a list in the `ein:$notebook-worksheets` slot.
+
 ** Notebooklist Buffer
 ** Kernel communication
 ** Contents API
@@ -65,3 +72,20 @@ What needs to be done:
    ~input-prompt-number~.
 4. Call ~ein:cell-goto~ on that cell. May need to swap buffers first.
 
+** Return of worksheets
+
+tkf/ein and IPython 2.x allowed for multiple worksheets within an individual
+notebook. This feature was removed in 3.0 since multiple worksheets do not make
+much sense in the context of a tabbed web browser interface. EIN's legacy code
+still supports worksheets, though at the moment that information is lost upon
+saving a notebook.
+
+Having multiple worksheet support makes some sense for ein; below is thinking on
+how to reimplement this feature.
+
+IPython nbformat 4 specifies a [[http://ipython.org/ipython-doc/3/notebook/nbformat.html#metadata][metadata]] key which can be used to store general
+information. Cell metadad has a tag key which is a "A list of string tags on the
+cell. Commas are not allowed in a tag."
+
+Best place to set the tag key is when generating [[content]] for saving a notebook.
+
diff --git a/lisp/ein-cell.el b/lisp/ein-cell.el
index 3af75d4..cb2c43b 100644
--- a/lisp/ein-cell.el
+++ b/lisp/ein-cell.el
@@ -1001,8 +1001,9 @@ prettified text thus be used instead of HTML type."
 (defun ein:output-property-p (maybe-property)
   (assoc maybe-property ein:output-type-map))
 
-(defmethod ein:cell-to-nb4-json ((cell ein:codecell) &optional discard-output)
-  (let ((metadata `((collapsed . ,(if (oref cell :collapsed) t json-false))))
+(defmethod ein:cell-to-nb4-json ((cell ein:codecell) wsidx &optional discard-output)
+  (let ((metadata `((collapsed . ,(if (oref cell :collapsed) t json-false))
+                    (tags . ((format "worksheet-%s" wsidx)))))
         (outputs (if discard-output []
                    (oref cell :outputs)))
         (renamed-outputs '())
@@ -1068,16 +1069,18 @@ prettified text thus be used instead of HTML type."
   `((cell_type . ,(oref cell :cell-type))
     (source    . ,(ein:cell-get-text cell))))
 
-(defmethod ein:cell-to-nb4-json ((cell ein:textcell) &optional discard-output)
+(defmethod ein:cell-to-nb4-json ((cell ein:textcell) wsidx &optional discard-output)
   `((cell_type . ,(oref cell :cell-type))
     (source    . ,(ein:cell-get-text cell))
-    (metadata . ((collapsed . t)))))
+    (metadata . ((collapsed . t)
+                 (tags . (,(format "worksheet-%s" wsidx)))))))
 
-(defmethod ein:cell-to-nb4-json ((cell ein:headingcell) &optional discard-output)
+(defmethod ein:cell-to-nb4-json ((cell ein:headingcell) wsidx &optional discard-output)
   (let ((header (make-string (oref cell :level) ?#)))
     `((cell_type . "markdown")
       (source .  ,(format "%s %s" header (ein:cell-get-text cell)))
-      (metadata . ((collapsed . t))))))
+      (metadata . ((collapsed . t)
+                   (tags . (,(format "worksheet-%s" wsidx))))))))
 
 (defmethod ein:cell-to-json ((cell ein:headingcell) &optional discard-output)
   (let ((json (call-next-method)))
diff --git a/lisp/ein-notebook.el b/lisp/ein-notebook.el
index 8419156..7bc342d 100644
--- a/lisp/ein-notebook.el
+++ b/lisp/ein-notebook.el
@@ -636,8 +636,13 @@ of NOTEBOOK."
 
 (defun ein:write-nbformat4-worksheets (notebook)
   (ein:log 'info "Writing notebook %s as nbformat 4." (ein:$notebook-notebook-name notebook))
-  (let ((all-cells (first (mapcar #'ein:worksheet-to-nb4-json
-                                  (ein:$notebook-worksheets notebook)))))
+  (let ((all-cells 
+                   (loop for ws in (ein:$notebook-worksheets notebook)
+                         for i from 0
+                         append (ein:worksheet-to-nb4-json ws i))
+                    ;; (mapcar #'ein:worksheet-to-nb4-json
+                    ;;               (ein:$notebook-worksheets notebook))
+                    ))
     `((metadata . ,(ein:aif (ein:$notebook-metadata notebook)
                        it
                      (make-hash-table)))
@@ -649,33 +654,7 @@ of NOTEBOOK."
                         'notebook_saving.Notebook)
     (ein:content-save content
                       #'ein:notebook-save-notebook-success
-                      (list notebook callback cbargs))
-    ;; (let ((data (ein:content-to-json content)))
-    ;;   ;; (push `(path . ,(ein:$notebook-notebook-path notebook)) data)
-    ;;   ;; (push `(name . ,(ein:$notebook-notebook-name notebook)) data)
-    ;;   ;; (push `(type . "notebook") data)
-    ;;   (ein:query-singleton-ajax
-    ;;    (list 'notebook-save
-    ;;          (ein:$notebook-url-or-port notebook)
-    ;;          (ein:$notebook-notebook-path notebook)
-    ;;          (ein:$notebook-notebook-name notebook))
-    ;;    (ein:notebook-url notebook)
-    ;;    :timeout ein:notebook-querty-timeout-save
-    ;;    :type "PUT"
-    ;;    :headers '(("Content-Type" . "application/json"))
-    ;;    :data data
-    ;;    :error (apply-partially #'ein:notebook-save-notebook-error notebook)
-    ;;    :success (apply-partially #'ein:notebook-save-notebook-workaround
-    ;;                              notebook retry callback cbarg)
-    ;;    :status-code
-    ;;    `((200 . ,(apply-partially
-    ;;               (lambda (notebook callback cbarg &rest rest)
-    ;;                 (apply #'ein:notebook-save-notebook-success
-    ;;                        notebook rest)
-    ;;                 (when callback
-    ;;                   (apply callback cbarg rest)))
-    ;;               notebook callback cbarg)))))
-    ))
+                      (list notebook callback cbargs))))
 
 (defun ein:notebook-save-notebook-command ()
   "Save the notebook."
diff --git a/lisp/ein-worksheet.el b/lisp/ein-worksheet.el
index 71f6bc5..ba3b225 100644
--- a/lisp/ein-worksheet.el
+++ b/lisp/ein-worksheet.el
@@ -242,12 +242,12 @@ current buffer."
     `((cells . ,(apply #'vector cells))
       ,@(ein:aand (oref ws :metadata) `((metadata . ,it))))))
 
-(defmethod ein:worksheet-to-nb4-json ((ws ein:worksheet))
+(defmethod ein:worksheet-to-nb4-json ((ws ein:worksheet) wsidx)
   (let* ((discard-output-p (oref ws :discard-output-p))
          (cells (ein:with-possibly-killed-buffer (ein:worksheet-buffer ws)
                   (mapcar (lambda (c)
                             (ein:cell-to-nb4-json
-                             c (ein:funcall-packed discard-output-p c)))
+                             c wsidx (ein:funcall-packed discard-output-p c)))
                           (ein:worksheet-get-cells ws)))))
     cells))