This chapter describes hardware and application profiling tools used by researchers and application developers. With over 30 years of research, there have been numerous tools developed and used, and it will be too difficult to include all of them here. Therefore, in this chapter, we describe various areas with a selection of widely accepted and recent tools. This chapter is intended for the beginning reader interested in exploring more about these topics. Numerous references are provided to help jump-start the interested reader into the area of hardware simulation and application profiling. We make an effort to clarify and correctly classify application profiling tools based on their scope, interdependence, and operation mechanisms. To visualize these features, we provide diagrams that explain various development relationships between interdependent tools. Hardware simulation tools are described into categories that elaborate on their scope. Therefore, we have covered areas of single to full-system simulation, power modeling, and network processors.