I will introduce recent work on the applications of magnetic nanoparticles in medicine and nanotechnology. This talk will focus primarily on in vitro applications, including methods for separating, printing, and manipulating various materials inside fluids. In the process, I will demonstrate how both magnetic and nonmagnetic materials can be manipulated above a substrate using a programmable template of magnets, such as those utilized in the data storage industry. In addition, I will touch on some of the in vivo applications of magnetic nanoparticles and magnetic stents in drug delivery. Throughout this talk, I will point out critical differences between self-assembly mechanisms occurring at the molecular versus mesoscopic length scales and investigate the fundamental limits for field-assisted self-assembly.