Kriek’s presentation will give a broad view of galaxies as the building blocks of the Universe; massive structures that contain up to 100s of billions of stars. Galaxies in today's Universe show a striking diversity among their properties, with large variations in their appearance, age, size, weight, and stellar birth rate. Despite this diversity, galaxies can broadly be divided into two types: low-mass spiral galaxies with high stellar production rates, and massive old elliptical galaxies in which no new stars are being formed. This broad distinction was already recognized by Edwin Hubble in the 1920s, yet it has remained puzzling as to how the different galaxy classes originated and how they may be related to each other. Kriek’s talk will cover this issue and present the current view of how the different types of galaxies may have formed and have evolved over cosmic time.