This introductory article reviews the topics covered in this issue of MRS Bulletin on New Developments in Colloid Science. Colloidal particles have a long history of importance in a broad range of applications in technology and materials processing. They can be made from many different materials and suspended in a wide variety of solvents. The rheological properties of colloidal suspensions have traditionally been of primary concern in their technological applications, and our understanding of these properties continues to evolve. However, new uses of colloidal particles are also emerging. Because they can be produced to a precise size, colloidal particles are now also being used in novel ways as building blocks for engineering completely new materials, including high-precision filters, controlled-porosity substrates, and photonic devices. In addition, new methods are evolving to alter the shape of the particles and create controlled structures with nonspherical particles. New experimental techniques are allowing improved measurement and increased understanding of the structure, properties, and behavior of colloidal suspensions. Significant progress continues to be made, and the potential uses of colloidal particles continue to grow. This issue presents a snapshot summary of recent developments in this field.