  We present an analysis of spectrosopic and astrometric data from APOGEE-2 and
Gaia DR2 to identify structures towards the Orion Complex. By applying a
hierarchical clustering algorithm to the 6-dimensional stellar data, we
identify spatially and/or kinematically distinct groups of young stellar
objects with ages ranging from 1 to 12 Myr. We also investigate the star
forming history within the Orion Complex, and identify peculiar sub-clusters.
With this method we reconstruct the older populations in the regions that are
presently largely devoid of molecular gas, such as Orion C (which includes the
$\sigma$ Ori cluster), and Orion D (the population that traces Ori OB1a, OB1b,
and Orion X). We report on the distances, kinematics, and ages of the groups
within the Complex. The Orion D groups is in the process of expanding. On the
other hand, Orion B is still in the process of contraction. In $\lambda$ Ori
the proper motions are consistent with a radial expansion due to an explosion
from a supernova; the traceback age from the expansion exceeds the age of the
youngest stars formed near the outer edges of the region, and their formation
would have been triggered when they were half-way from the cluster center to
their current positions. We also present a comparison between the parallax and
proper motion solutions obtained by Gaia DR2, and those obtained towards
star-forming regions by Very Long Baseline Array.
