Cell-free gene expression (CFE) is a highly versatile experimental environment ideal to construct biochemical systems in vitro by executing either natural or synthetic gene circuits. CFE enables interrogating biochemical systems quantitatively and in isolation far from the complexity of real living cells. I will present several experiments that my lab has done recently using an E. coli CFE system. First, I will present this CFE system, what it is, what it does. In the second part of my talk, I will show how we construct synthetic cells using CFE. These minimal cells are convenient to uncover and quantify fundamental aspects of supramolecular assembly.