This book introduces Gravitational Microlensing, one of the techniques used for extrasolar planet searching and gives an overview of different methods used for extrasolar planet searching. It also gives a brief discussion regarding the Finite-Source Effect. The book covers single and binary lens microlensing events and describes caustics and critical curves by showing some examples of binary lens caustic crossing events and their light curves. A summary of some of the extrasolar planets discovered using gravitational microlensing is included, together with introductions to some of the data reduction methods, optimization techniques, and programs used for data analysis. A microlensing target observed during the 2011 observation season is also introduced and discussed in the book.