In this seminar, we will discuss developments in the extraction of parton distribution functions (PDFs). We will focus on pion PDFs, which have received renewed interest thanks to the advent of lattice data and the promise of future experimental data. Pion PDFs have also served as a sandbox for new methodologies in global QCD analyses, playing the dual role of determining the pion structure from data and preparing the ground for the application of modern statistical techniques to the more complex proton PDF analyses.