  Stars form predominantly in clusters inside dense clumps of turbulent,
magnetized molecular clouds. The typical size and mass of the cluster-forming
clumps are \sim 1 pc and \sim 10^2 - 10^3 M_\odot, respectively. Here, we
discuss some recent progress on theoretical and observational studies of
clustered star formation in such parsec-scale clumps with emphasis on the role
of protostellar outflow feedback. Recent simulations indicate that protostellar
outflow feedback can maintain supersonic turbulence in a cluster-forming clump,
and the clump can keep a virial equilibrium long after the initial turbulence
has decayed away. In the clumps, star formation proceeds relatively slowly; it
continues for at least several global free-fall times of the parent dense clump
(t_{ff}\sim a few x 10^5 yr). The most massive star in the clump is formed at
the bottom of the clump gravitational potential well at later times through the
filamentary mass accretion streams that are broken up by the outflows from
low-mass cluster members. Observations of molecular outflows in nearby
cluster-forming clumps appear to support the outflow-regulated cluster
formation model.
