The specificity and reversibility of the hydrogen-bonding between two complementary strands in DNA make this bio-molecule a unique binding agent. When DNA is grafted to nano-and micrometer sized colloids it can lead to specific binding between particles coated with complementary strands of single-stranded DNA. DNA-coated colloids hold great promise as the building blocks of a new generation of complex, self-assembling colloidal materials. This brief review sketches the recent developments and present status of the research on DNA-coated colloids with special emphasis on their role as potential building blocks in complex, self-assembling materials and as highly sensitive bio-sensors. Although the present review cannot be comprehensive, it hopefully highlights the promise of DNA-coated colloids as versatile and still largely unexplored form of soft matter.