diff --git a/.travis.yml b/.travis.yml
new file mode 100644
index 0000000..b71cfbb
--- /dev/null
+++ b/.travis.yml
@@ -0,0 +1,12 @@
+language: python
+python:
+  - "3.6"
+  - "3.7-dev"  # 3.7 development branch
+before_install:
+  - cd fields_overlap
+# command to install dependencies
+install:
+  - pip install -r requirements.txt
+# command to run tests
+script:
+  - pytest
diff --git a/fields_overlap/overlap.py b/fields_overlap/overlap.py
new file mode 100644
index 0000000..b024be3
--- /dev/null
+++ b/fields_overlap/overlap.py
@@ -0,0 +1,65 @@
+import matplotlib.pyplot as plt
+from matplotlib.path import Path
+import matplotlib.patches as patches
+
+def show_fields(field1, field2):
+    def vertices(left, bottom, right, top):
+        verts = [(left, bottom), (left, top), (right, top), (right, bottom), (left, bottom)]
+        return verts
+
+    codes = [Path.MOVETO, Path.LINETO, Path.LINETO, Path.LINETO, Path.CLOSEPOLY]
+    path1 = Path(vertices(*field1), codes)
+    path2 = Path(vertices(*field2), codes)
+    fig = plt.figure()
+    ax = fig.add_subplot(111)
+    patch1 = patches.PathPatch(path1, facecolor='orange', lw=2)
+    patch2 = patches.PathPatch(path2, facecolor='blue', lw=2)
+    ax.add_patch(patch1)
+    ax.add_patch(patch2)
+    ax.set_xlim(0, max(*field1, *field2) + 1)
+    ax.set_ylim(0, max(*field1, *field2) + 1)
+    fig.show()
+
+
+def overlap_area(field1, field2):
+    '''
+    Calculates the area of overlapping fields from the coordinates
+    of their corners.
+
+    parameters
+    ----------
+    field1: (tuple | list) of (int | float)
+        Coordinates of the first field. Order should be: (left, bottom, right, top)
+
+    field2: (tuple | list) of (int | float)
+        Coordinates of the second field. Order should be: (left, bottom, right, top)
+
+    Returns
+    -------
+    int or float
+        Area in the coordinates entered unit.
+
+    Example
+    -------
+    >>> from overlap import overlap_area
+    >>> field_a = (1, 1, 4, 4) # position in kms as (x_0, y_0, x_1, y_1)
+    >>> field_b = (2, 2, 3, 3) # smaller field inside field_a
+    >>> overlap_area(field_a, field_b)
+    1
+
+    '''
+
+    left1, bottom1, right1, top1 = field1
+    left2, bottom2, right2, top2 = field2
+
+    if (left1 > right1 or bottom1 > top1 or
+        left2 > right2 or bottom2 > top2):
+        raise ValueError(" Coordinates need to be entered (left, bottom, right, top)")
+
+    overlap_left = max(left1, left2)
+    overlap_bottom = max(bottom1, bottom2)
+    overlap_right = min(right1, right2)
+    overlap_top = min(top1, top2)
+    overlap_height = max(0, overlap_top - overlap_bottom)
+    overlap_width = max(0, overlap_right - overlap_left)
+    return overlap_height * overlap_width
diff --git a/fields_overlap/pytest.ini b/fields_overlap/pytest.ini
new file mode 100644
index 0000000..446b3ff
--- /dev/null
+++ b/fields_overlap/pytest.ini
@@ -0,0 +1,2 @@
+[pytest]
+addopts = --cov=overlap --cov-report html --doctest-modules
diff --git a/fields_overlap/requirements.txt b/fields_overlap/requirements.txt
new file mode 100644
index 0000000..5e9b7af
--- /dev/null
+++ b/fields_overlap/requirements.txt
@@ -0,0 +1,3 @@
+pytest==3.2.0
+pytest-cov==2.6.0
+matplotlib==2.0.2
diff --git a/fields_overlap/test_overlap.py b/fields_overlap/test_overlap.py
new file mode 100644
index 0000000..a5811cd
--- /dev/null
+++ b/fields_overlap/test_overlap.py
@@ -0,0 +1,80 @@
+from pytest import approx, raises
+
+from overlap import overlap_area
+
+def test_basic():
+    ''' Tests that basic example works '''
+    big_field = (1, 1, 4, 4)
+    inner_field = (2, 2, 3, 3)
+    assert overlap_area(big_field, inner_field) == 1
+
+
+def test_partial_overlap():
+    ''' Tests when there's a partial overlap'''
+    base_field = (1, 1, 4, 3)
+    over_field = (2, 2, 3, 4)
+    assert overlap_area(base_field, over_field) == 1
+
+
+def test_corner_overlap():
+    ''' Test when there is a box in a corner'''
+    base_field = (1, 0, 3, 5)
+    over_field = (2, 4, 4, 6)
+    assert overlap_area(base_field, over_field) == 1
+
+
+def test_edge_touching():
+    ''' Test when there is an edge '''
+    base_field = (1, 1, 4, 4)
+    over_field = (2, 2, 3, 4)
+    assert overlap_area(base_field, over_field) == 2
+
+
+def test_2opposite_edge_touching():
+    ''' Test when there is an edge '''
+    base_field = (1, 1, 4, 4)
+    over_field = (2, 1, 3, 4)
+    assert overlap_area(base_field, over_field) == 3
+
+
+def test_outside_edge_touching():
+    ''' Test when they are touching on the outside '''
+    base_field = (1, 1, 4, 4)
+    over_field = (2, 4, 3, 5)
+    assert overlap_area(base_field, over_field) == 0
+
+
+def test_no_overlap():
+    ''' Test when they are not touching each other '''
+    base_field = (0, 0, 3, 3)
+    over_field = (4, 4, 5, 5)
+    assert overlap_area(base_field, over_field) == 0
+
+
+def test_floats():
+    ''' Test that still works when using floats '''
+    base_field = (1, 1., 3.5, 3.5)
+    over_field = (3, 3, 5, 5)
+    assert overlap_area(base_field, over_field) == 0.5 * 0.5
+
+
+def test_floats_again():
+    ''' Test that still works when using floats '''
+    base_field = (1, 1., 3.3, 3.1)
+    over_field = (3, 3, 5, 5)
+    assert overlap_area(base_field, over_field) == approx(0.3 * 0.1, rel=1e-3)
+
+
+def test_negative_basic():
+    ''' Tests that basic example works '''
+    big_field = (-1, -1, -4, -4)
+    inner_field = (-2, -2, -3, -3)
+    with raises(ValueError, message=" Coordinates need to be entered (left, bottom, right, top) "):
+        overlap_area(big_field, inner_field)
+
+
+def test_negative_basic2():
+    ''' Tests that basic example works '''
+    big_field = (-1, -1, 1, 1)
+    inner_field = (0, -2, 1, 2)
+    assert overlap_area(big_field, inner_field) == 2