This document summarizes an application portfolio rationalization methodology based on a book by Prashant Halari, Sushil Paigankar, Hitesh Salla, and Rajaram Vengurlekar. The methodology aims to establish a quantitative baseline to make prudent management decisions regarding applications. It ensures proper business-IT alignment by prioritizing applications that need attention and determining management options. The methodology involves selecting participants, collecting data, analyzing applications, categorizing them, validating categorizations with stakeholders, and developing a roadmap. Lessons learned include treating it as a broader decision process and measuring applications over their lifecycles.