diff --git a/conway.hy b/conway.hy
new file mode 100644
index 0000000..ae2cb4c
--- /dev/null
+++ b/conway.hy
@@ -0,0 +1,56 @@
+(import grid)
+(import-from functools reduce)
+(import-from operator add)
+
+
+(def *world* (grid.Torus 10 10))
+
+
+(defun sum (ns)
+  (reduce add ns))
+
+
+(defun set! (world x y value)
+  (setv (get world (, x y)) value))
+
+
+(defun get! (world x y)
+  (get *world* (, x y)))
+
+
+(defun neighbours (world x y)
+  (sum (list-comp
+        (get! world (+ x dx) (+ y dy))
+         (dx [-1 0 1]
+          dy [-1 0 1])
+        (!= (, (+ x dx) (+ y dy)) (, x y)))))
+
+
+(defun step (world)
+  (let ((new-world (.copy grid.Torus world)))
+    (for (x (range new-world.width))
+         (for (y (range new-world.height))
+              (let ((cell (get! new-world x y))
+                    (ns (neighbours world x y)))
+                (if (= cell 1)
+                    (cond ((< ns 2) (set! new-world x y 0))
+                          ((or (= ns 2) (= ns 3)) (set! new-world x y 1))
+                          ((> ns 3) (set! new-world x y 0)))
+                    (cond ((= ns 3) (set! new-world x y 1))
+                          (True (set! new-world x y 0)))))))
+    new-world))
+
+
+
+;; Create a glider...
+(set! *world* 4 2 1)
+(set! *world* 5 3 1)
+(set! *world* 3 4 1)
+(set! *world* 4 4 1)
+(set! *world* 5 4 1)
+
+;; Cycle through once...
+(for (_ (range 5))
+     (.pprint grid.Torus *world*)
+     (setv *world* (step *world*))
+     (print))
diff --git a/grid.py b/grid.py
new file mode 100644
index 0000000..c1248ee
--- /dev/null
+++ b/grid.py
@@ -0,0 +1,172 @@
+from collections import Mapping
+from copy import deepcopy
+
+
+class Grid(Mapping):
+    """
+    A Grid is a two-dimensional data-structure.
+
+    >>> g = Grid(5, 5)
+    >>> Grid.pprint(g)
+    0 0 0 0 0
+    0 0 0 0 0
+    0 0 0 0 0
+    0 0 0 0 0
+    0 0 0 0 0
+    >>> g[0, 0] = 1
+    >>> g[4, 4] = 1
+    >>> Grid.pprint(g)
+    1 0 0 0 0
+    0 0 0 0 0
+    0 0 0 0 0
+    0 0 0 0 0
+    0 0 0 0 1
+
+    The height and width of the grid are inclusive while the indexing
+    begins at zero.  Access to elements of the grid are provided via
+    the Mapping interface.  Internally the elements are stored in a
+    flat array and can be any Python object.  The default element is
+    the integer 0, but can be specified via the 'value' parameter to
+    the Grid's constructor:
+
+    >>> g = Grid(3, 3, value=".")
+    >>> Grid.pprint(g)
+    . . .
+    . . .
+    . . .
+
+    There are helpful static methods available for copying grids,
+    creating grids from arrays, and pretty printing grids.
+
+    >>> w = h = 3
+    >>> world = [0, 0, 0,
+    ...          1, 0, 1,
+    ...          0, 1, 0]
+    >>> g = Grid.from_array(w, h, world)
+    >>> Grid.pprint(g)
+    0 0 0
+    1 0 1
+    0 1 0
+
+    Care must be taken when creating Grids from arrays to ensure that
+    the proper dimensions are passed in.  The only assertion this
+    method makes is that the product of the width and height are the
+    same as the length of the input array.
+
+    Grids can be compared for equality:
+
+    >>> g1 = Grid(3, 3)
+    >>> g2 = Grid(3, 3)
+    >>> g1[0, 0] = 1
+    >>> g2[0, 0] = 1
+    >>> g3 = Grid(3, 3)
+    >>> g1 == g2
+    True
+    >>> g1 == g3
+    False
+    """
+
+    def __init__(self, width, height, value=0):
+        self.width = width
+        self.height = height
+        self._grid = [value for _ in range(width * height)]
+
+    @classmethod
+    def copy(cls, other):
+        g = cls(other.width, other.height)
+        g._grid = deepcopy(other._grid)
+        return g
+
+    @classmethod
+    def from_array(cls, width, height, arr, copy=True):
+        assert len(arr) == width * height, ("Array dimensions do not "
+                                            "match length of array.")
+        g = cls(width, height)
+        a = deepcopy(arr) if copy else arr
+        g._grid = a
+        return g
+
+    @staticmethod
+    def pprint(grid):
+        for y in range(grid.height):
+            print(" ".join(str(grid[x, y]) for
+                           x in range(grid.width)))
+
+    def _is_valid_location(self, x, y):
+        if x < 0 or x > self.width - 1:
+            return False
+        if y < 0 or y > self.height - 1:
+            return False
+        return True
+
+    def __len__(self):
+        return self.width * self.height
+
+    def __eq__(self, other):
+        assert isinstance(other, Grid)
+        return self._grid == other._grid
+
+    def __iter__(self):
+        return iter(self._grid)
+
+    def __contains__(self, value):
+        return value in self._grid
+
+    def __getitem__(self, *args):
+        if not self._is_valid_location(*args[0]):
+            raise KeyError("({0}, {1}) is an invalid co-ordinate".format(
+                *args[0]))
+        try:
+            return self._grid[args[0][1] * self.height + args[0][0]]
+        except IndexError:
+            raise KeyError("({0}, {1}) is an invalid co-ordinate".format(
+                *args[0]))
+
+    def __setitem__(self, *args):
+        if not self._is_valid_location(*args[0]):
+            raise KeyError("({0}, {1}) is an invalid co-ordinate".format(
+                *args[0]))
+        try:
+            self._grid[args[0][1] * self.height + args[0][0]] = args[1]
+        except IndexError:
+            raise KeyError("({0}, {1}) is an invalid co-ordinate".format(
+                *args[0]))
+
+
+class Torus(Grid):
+    """
+    A grid whose edges are connected.
+
+    >>> w = h = 3
+    >>> world = [0, 1, 0,
+    ...          0, 0, 0,
+    ...          0, 2, 0]
+    >>> t = Torus.from_array(w, h, world)
+    >>> Torus.pprint(t)
+    0 1 0
+    0 0 0
+    0 2 0
+    >>> t[1, 0]
+    1
+    >>> t[1, -1]
+    2
+    >>> t[4, 0]
+    1
+    """
+
+    def __getitem__(self, *args):
+        x = args[0][0] % self.width
+        y = args[0][1] % self.height
+
+        return self._grid[y * self.height + x]
+
+    def __setitem__(self, *args):
+        x = args[0][0] % self.width
+        y = args[0][1] % self.height
+
+        self._grid[y * self.height + x] = args[1]
+
+
+if __name__ == "__main__":
+    import doctest
+    doctest.testmod()