In recent years, the rapid development and progress of single-molecule dete
ction techniques have opened up a new era of biological research. The advan
tage of single-molecule studies is that data are not obscured by the ensemb
le-averaged measurements inherent in classical biochemical experiments. The
se techniques are shedding light on the dynamic and mechanistic properties
of molecular machines, both in vivo and in vitro. This review summarizes th
e single-molecule experiments that have been designed to investigate molecu
lar motors, enzyme reactions, protein dynamics, DNA transcription and cell
signaling.