This study guide was first published as a GEMINI technical note by ACCION International. It was written by Katherine Stearns. It is a straightforward and easy to follow exposition of the role of interest rates from a borrower’s and a lender’s perspective. It explains the differences between nominal, effective and real interest rates and shows how each of these can be calculated. The guide also examines how lenders can establish interest rates and fees structures to ensure self-sufficiency of the institution. The study guide ends with a set of questions and problems which can be worked through to reinforce the points covered in the lessons.