Gas-filled microbubbles, with the size of several micrometres, are strong scatterers of ultrasound waves used in diagnostic imaging. Application of these microbubbles as ultrasound contrast materials is discussed, in view of the design of materials capable of selectively targeting the diseased tissues/organs. Methods of preparation, mechanisms of action, biodistribution and stability in vitro and in vivo are reviewed. Targeted microbubbles with various ligands (antibodies, peptides) attached to the shells have been prepared and tested in vitro and in vivo. Examples of specific application in diagnostic imaging and possible therapeutic use are discussed.