  Transitional millisecond pulsars (tMSPs), which are systems that harbor a
pulsar in the throes of the recycling process, have emerged as a new source
class since the discovery of the first such system a decade ago. These systems
switch between accretion-powered low-mass X-ray binary (LMXB) and
rotation-powered radio millisecond pulsar (RMSP) states, and provide exciting
avenues to understand the physical processes that spin-up neutron stars to
millisecond periods. During the last decade, three tMSPs, as well as a
candidate source, have been extensively probed using systematic,
multi-wavelength campaigns. Here we review the observational highlights from
these campaigns and our general understanding of tMSPs.
