“95% of the words are spent extolling the benefits of ‘modularity’ and that little, if anything, is said about how to achieve it” - Glenford J. Myers, 1978. This quote is 40 years old. Today, 4 decades later, nothing has changed except terminology. Time to change this. I want to talk about the various strategies of decomposing systems into modular components. You will learn what exactly Bounded Contexts and Microservices are, and what are the differences between the two notions. We will analyze what happens between services - how data flows, and how these flows can be optimized. Ultimately, we will explore different decomposition strategies and heuristics for designing modular systems - systems that aren’t driven by ever-changing fads, but by your business needs.