  We present an overview of the LOFAR Tied-Array All-Sky Survey (LOTAAS) for
radio pulsars and fast transients. The survey uses the high-band antennas of
the LOFAR Superterp, the dense inner part of the LOFAR core, to survey the
northern sky (dec > 0 deg) at a central observing frequency of 135 MHz. A total
of 219 tied-array beams (coherent summation of station signals, covering 12
square degrees), as well as three incoherent beams (covering 67 square degrees)
are formed in each survey pointing. For each ofthe 222 beams, total intensity
is recorded at 491.52 us time resolution. Each observation integrates for 1 hr
and covers 2592 channels from 119 to 151 MHz. This instrumental setup allows
LOTAAS to reach a detection threshold of 1 to 5 mJy for periodic emission. Thus
far, the LOTAAS survey has resulted in the discovery of 73 radio pulsars. Among
these are two mildly recycled binary millisecond pulsars (P = 13 and 33 ms), as
well as the slowest-spinning radio pulsar currently known (P = 23.5 s). The
survey has thus far detected 311 known pulsars, with spin periods ranging from
4 ms to 5.0 s and dispersion measures from 3.0 to 217 pc/cc. Known pulsars are
detected at flux densities consistent with literature values. We find that the
LOTAAS pulsar discoveries have, on average, longer spin periods than the known
pulsar population. This may reflect different selection biases between LOTAAS
and previous surveys, though it is also possible that slower-spinning pulsars
preferentially have steeper radio spectra. LOTAAS is the deepest all-sky pulsar
survey using a digital aperture array; we discuss some of the lessons learned
that can inform the approach for similar surveys using future radio telescopes
such as the Square Kilometre Array.
