RNA is an ancient and highly versatile molecule that plays fundamental roles in all living organisms. Its molecular functions range from being a mediator of genetic information to the regulation of essential cellular processes. These functions are often accomplished in close association with RNA binding proteins. Over the past few years, a considerable number of high-resolution three-dimensional structures of important protein-RNA complexes have been determined. Here, we wish to discuss recent examples and highlight principles and distinct features of single-stranded RNA recognition by conserved RNA binding domains.