This document summarizes the Boston Consulting Group's product portfolio matrix model, which helps firms decide how much to invest in product lines based on their market share and growth rate. The matrix categorizes product lines as stars, cash cows, dogs, or question marks. It then provides recommendations for investment, development, or divestment for each category based on their relative market share and growth. The model is meant to help firms allocate resources but has some limitations in only using two factors and assuming independence between product lines.