The Ansoff Matrix is a simple framework to categorise different growth options for the business.
It is a 2×2 matrix with existing and new customers and products as the axes, invented by Igor Ansoff
The assumption underlying this framework is that the competitive advantage of most businesses will either rest in their investment in product development or their customer relationships. Companies should explore growth options leveraging each of these separately. Conventional wisdom is that businesses should avoid opportunities in the new business venture segment (also called diversification) that does not leverage either of these.
When is it useful?
The Ansoff Matrix is a useful as an introduction to strategic thinking since it it very easy to understand and apply.
Use it as an easy structure when you want to brainstorm growth opportunities.
I want to know more
A more advanced version of this framework is the Product/Matrix matrix. It is based of the same principle of leveraging your existing product development investment and customer relationships, it breaks the opportunities down to more specifics.
Look also at Growth Adjacencies tool, which includes these growth options and adds more dimensions.