Ultrasound imaging is among the most used tomographic imaging modalities and often the first diagnostic method a patient is confronted with. Although most examinations do not require the use of contrast agents, it has been shown that these may help in oncology for tumor detection, characterisation, therapy monitoring and for sentinel lymph node imaging. In cardiovascular diseases, contrast agents help to characterise inflammatory and atherosclerotic lesions in the vascular wall and to assess tissue perfusion.This book chapter gives an overview on the composition of different microbubble types, which are used as ultrasound contrast agents. It also reports how these can be modified to specifically bind to targets at the vasculature, thus forming molecular imaging probes. In addition, a detailed description of microbubble detection techniques and of methods to assess relative blood volume and perfusion and to quantify the amount of stationary microbubbles at the vascular wall is given. Finally, examples for the use of functional and molecular ultrasound imaging in oncology and cardiovascular diseases illustrate important application fields and emphasize the great potential of this imaging technology.