For years, we’ve known what’s been weighing down our responsive pages: images. Huge ones, specially catered to huge screens, which we’ve been sending to everyone. We’ve known how to fix this problem for a while too: let us send different sources to different clients. New markup allows us to do exactly that. srcset lets us offer multiple versions of an image to browsers, which, with a little help from sizes, pick the most appropriate source to load out of the bunch. picture and source let us step in and exert a bit more control, ensuring that certain sources will be picked based on either media queries or file type support.