  A low mass X-ray binary (LMXB) contains either a neutron star or a black hole
accreting materials from its low mass companion star. It is one of the primary
astrophysical sources for studying the stellar size compact objects and the
accreting phenomena. As with other binary systems, the most important parameter
of an LMXB is the orbital period, which allows us to learn about the nature of
the binary system and constrain the properties of the system's components,
including the compact object. As a result, measuring the orbital periods of
LMXBs is essential for investigating these systems even though fewer than half
of them have known orbital periods. This article introduces the different
methods for measuring the orbital periods in the X-ray band and reviews their
application to various types of LMXBs, such as eclipsing and dipping sources,
as well as pulsar LMXBs.
