Small animal Positron Emission Tomography (PET) is being utilized in animal models of a wide variety of diseases including cancer, cardiac disease, pulmonary disease and neurological diseases. High sensitivity/high resolution small animal PET scanners are currently commercially available allowing imaging utilizing multiple radiopharmaceuticals and consecutive imaging over relatively long time frames. Examples from the types of disease models listed above will be given. One of the major challenges in small animal PET imaging is the conversion of qualitative image data into quantitative parametric images. In order to accomplish this arterial time activity curves need to be measured and in the majority of cases tracer metabolism quantified. Accomplishing this as a major challenge particularly when utilizing mouse models of diseases. Approaches to quantify cardiac blood flow and metabolism will be presented to show how quantitative data can be obtained. There is currently great interest in the application of nanoparticles as delivery vehicles both for diagnostic agents and therapeutic drugs. MicroPET imaging has played a role in the evaluation of the pharmacokinetics of these novel agents. Examples of this application will be presented. Radiopharmaceuticals utilized with small animal PET scanners range from small molecules to labeled peptides to labeled antibodies and to the nanoparticles discussed above. Examples of imaging of all of these types of agents will be presented.