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The Orion OB1 stellar association is a contingent group of several dozen hot giant stars of spectral types O and B. Associated are thousands of lower-mass stars, and a (smaller but significant) number of protostars. It is part of the larger Orion Molecular Cloud Complex. Owing to its relative closeness and complexity it is the most closely studied OB association.

Structure
"OB Associations play an important role in the large scale propagation of star formation and in the shaping and evolution of the interstellar medium".

The Orion OB1 association consists of the following subgoups:
 * Orion OB1a - the group of stars northwest of the Orion Belt stars with an average age of about 12 million years. Within this sub-group is a sub-association known as the 25 Orionis group.
 * Orion OB1b - the three bright stars ζ Ori (Alnitak), ε Ori (Alnilam), and δ Ori (Mintaka) which make up the asterism known as "Orion's Belt", and minor stars. This group has an average age of approximately 8 million years is further subdivided into three subgroups.
 * Orion OB1c - the stars in Orion's Sword, 3-6 million years old
 * Orion OB1d - the stars of the Orion Nebula and M43 (the youngest stars)

Signatures of stellar debris disk evolution have been detected in the 1a and 1b subgroups.