The Lake Simcoe drainage basin is located in Southern Ontario, approximately 25 km north of Metropolitan Toronto. It occupies 3592 km2with the land portion representing approximately 80% of the total area. The largest portion of the drainage basin is located to the south of Lake Simcoe in an area where streams flow north into the lake through a landscape highly modified by agricultural and urban activity. The entire basin is located in a transitional portion of the Southern Ontario landscape. In the southerly two thirds, deep fertile soils were deposited by glacial activity on top of limestone and shale bedrock. In the northerly third, thin soils are sparsely spread over a limestone, shale and granitic bedrock that has been exposed and eroded in many places by glacial action. The transitional nature of the basin, a varied geological past and over 200 years of intensive exploitation by European immigrants have created a complex ecological tapestry. The paper briefly explores the fundamental biophysical features and attributes of the basin.