A great deal of experimental and theoretical progress has been achieved in
our understanding of partonic structure of hadrons in recent decades. 
I will discuss our current understanding  and will emphasize the emerging 
concept of 3D (three-dimensional) parton distributions and discuss their 
formal definition, evolution, and phenomenology.  Jefferson Lab 12 will play crucial 
role in experimental measurements of hadron structure. I will explain details of the 
program and show the potential of future measurements. I will also discuss future of 
nuclear physics beyond Jefferson Lab 12 at a proposed Electron-Ion Collider.