This document discusses building performance monitoring tools for VMware vSphere using the vSphere APIs. It begins with an overview of common use cases for monitoring CPU, memory, disk, and network performance. These include monitoring high CPU ready times, memory ballooning vs swapping, disk latency, and network throughput. The document then covers techniques for building applications that collect performance data using the vSphere APIs. It provides examples of useful metrics and how to identify issues like CPU overcommitment. The target audience is described as system administrators and VMware partners looking to integrate performance monitoring into their own tools.