The rise of SoCs caused a paradigm shift on system design flow. The TLM methodology was created in the search for a new paradigm that could allow design representation at an intermediate level of abstraction between paper specification and RTL models. This chapter introduces the Transaction Level Modeling (TLM) design methodology. Its main goals are to explain the main concepts behind TLM and to show that it can work very well in SystemC-based designs. That is why we discuss the strong relation between SystemC and TLM and emphasize the main features in the recently released SystemC TLM 2.0 standard. As in Chap. 2, the intention is not to serve as a substitute for the reference manual. Instead, our focus is to provide a good understanting on the underlying ideas and to show how to put TLM to work in SystemC-based platform designs. We finalize this chapter with a simple platform example using the SystemC TLM standard. Following chapters will present more elaborate platform examples by relying on the main concepts and elements introduced in the first part of the book.