A Practice Note discussing the private equity "buy and build" strategy of acquiring an initial platform company (using a buyout transaction) followed by one or more strategic "add-on" (also called "bolt-on" or "tuck-in") acquisitions to grow the platform. This Note provides an overview of this strategy, a comparison of platform company add-ons versus traditional portfolio company acquisitions, a description of the customary structure and characteristics of add-on targets, and best practices for a successful buy and build program.