Colloidal nanocrystals are crystalline particles coated with a monolayer of surfactants whose outstanding physical properties have been the topic of intense research for 30 years. Semi-conducting nanocrystals or quantum dots have been the subject of the 2023 Nobel Prize in chemistry. I will first introduce these objects, detail their synthesis, and some of their optical properties, as well as some applications.  I will then focus on 2D semiconducting nanocrystals (nanoplatelets), which are my current research topic. I will detail their structure, bending, and rolling into complex (chiral) shapes and their self-assembly.