Abstract: Nanoparticles have found many applications in medical imaging and therapeutics in the past few years, resulting in the field of nanomedicine. Nanoparticles can offer advantages over small molecules, such as high payloads, long circulation times, ease of integration of multiple properties and superior accumulation in disease sites. Gold nanoparticles have many applications in medicine. We will discuss their use as x-ray based imaging agents and our progress towards engineering biodegradable and excretable gold nanoparticles. Recent results in the use of bismuth nanoparticles and silver nanoparticles as x-ray imaging contrast agents will also be reported. As alternatives to synthetic nanoparticles, we have developed lipoprotein based nanoparticles for delivery of contrast media and drugs. We will discuss innovations in this area, particularly for delivery of drugs to atherosclerotic plaques. Last we will discuss the exploitation of nanoparticle catalytic activity for imaging and therapy. Peroxidase-like activity can be used to create in vivo light release and to have anti-biofilm actions, eradicating infections.