diff --git a/package.json b/package.json
index 5b0d568..52bbef0 100644
--- a/package.json
+++ b/package.json
@@ -6,6 +6,7 @@
   "typings": "lib/index.d.ts",
   "dependencies": {
     "phosphor-observablelist": "^0.9.2",
+    "phosphor-signaling": "^1.1.2",
     "phosphor-widget": "^0.9.13"
   },
   "devDependencies": {
diff --git a/src/index.ts b/src/index.ts
index 9efd726..f40b9a5 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,3 +1,180 @@
 // Copyright (c) Jupyter Development Team.
 // Distributed under the terms of the Modified BSD License.
 'use-strict';
+
+import {
+  IInputAreaViewModel
+} from 'jupyter-js-input-area';
+
+import {
+  IOutputAreaViewModel
+} from 'jupyter-js-output-area';
+
+import {
+  IObservableList
+} from 'phosphor-observablelist';
+
+import {
+  ISignal
+} from 'phosphor-signaling';
+
+import {
+  Widget
+} from 'phosphor-widget';
+
+import './index.css';
+
+
+/**
+ * An enum which describes the type of cell.
+ */
+enum CellType {
+  /**
+   * The cell contains code input.
+   */
+  Code,
+
+  /**
+   * The cell contains markdown.
+   */
+  Markdown,
+
+  /**
+   * The cell contains raw text.
+   */
+  Raw
+}
+
+
+/**
+ * The arguments object emitted with the `stateChanged` signal.
+ */
+export
+interface ICellChangedArgs<T> {
+  name: string,
+  oldValue: T;
+  newValue: T;
+}
+
+
+/**
+ * An object which is serializable.
+ */
+export
+interface ISerializable {
+  toJSON(): any;
+  fromJSON(data: any): void;
+}
+
+
+/**
+ * The definition of a model object for a base cell.
+ */
+interface IBaseCellViewModel {
+
+  /**
+   * The type of cell.
+   */
+  type: CellType;
+
+  /**
+   * Tags applied to the cell.
+   */
+  tags?: IObservableList<string>;
+
+  /**
+   * Get namespaced metadata about the cell.
+   */
+  getMetadata(namespace: string) : IObservableMap<string, ISerializable>;
+
+  /**
+   * The input area of the cell.
+   */
+  input: IInputAreaViewModel;
+
+  /**
+   * Whether a cell is deletable.
+   */
+  deleteable: boolean;
+
+  /**
+   * Whether a cell is mergable.
+   */
+  mergeable: boolean;
+
+  /**
+   * Whether a cell is splittable.
+   */
+  splittable: boolean;
+
+  /**
+   * Whether a cell is rendered.
+   */
+  rendered: boolean;
+
+  /**
+   * Whether the cell is marked for applying commands
+   */
+  marked: boolean;
+
+  /**
+   * Run the cell.
+   */
+  run(): void;
+}
+
+
+/**
+ * The definition of a code cell.
+ */
+export
+interface ICodeCellViewModel extends IBaseCellViewModel {
+
+  /**
+   * A signal emitted when state of the cell changes.
+   */
+  stateChanged: ISignal<ICodeCellViewModel, ICellChangedArgs<any>>;
+
+  output: IOutputAreaViewModel;
+}
+
+
+/**
+ * The definition of a raw cell.
+ */
+export
+interface IRawCellViewModel extends IBaseCellViewModel {
+
+  /**
+   * A signal emitted when state of the cell changes.
+   */
+  stateChanged: ISignal<IRawCellViewModel, ICellChangedArgs<any>>;
+
+  /**
+   * The raw cell format.
+   */
+  format?: string;
+}
+
+
+/**
+ * The definition of a markdown cell.
+ */
+export
+interface IMarkdownCellViewModel extends IBaseCellViewModel {
+
+  /**
+   * A signal emitted when state of the cell changes.
+   */
+  stateChanged: ISignal<IMarkdownCellViewModel, ICellChangedArgs<any>>;
+}
+
+
+
+/**
+ * A model consisting of any valid cell type.
+ */
+export
+type ICellViewModel =  (
+  IRawCellViewModel | IMarkdownCellViewModel | ICodeCellViewModel
+);