Forrester recommends B2C and B2B marketing executives streamline and lead agency selection using Forrester’s agency partner lifecycle approach. A critical step in initiating the lifecycle is assembling a buying group to aid with decisioning and selection. Forrester developed the ABC Decisioning Tool to help marketers cast a team of anchors, buyers, and collaborators that help establish selection criteria, identify a shortlist of potential partners, evaluate, select, and eventually review the selected partner(s). This report describes how B2C and B2B marketing executives can use the ABC Decisioning Tool to lead a streamlined and successful selection and management process.