  The MiMeS project is a large-scale, high resolution, sensitive
spectropolarimetric investigation of the magnetic properties of O and early B
type stars. Initiated in 2008 and completed in 2013, the project was supported
by 3 Large Program allocations, as well as various programs initiated by
independent PIs and archival resources. Ultimately, over 4800 circularly
polarized spectra of 560 O and B stars were collected with the instruments
ESPaDOnS at the Canada-France-Hawaii Telescope, Narval at the T\'elescope
Bernard Lyot, and HARPSpol at the European Southern Observatory La Silla 3.6m
telescope, making MiMeS by far the largest systematic investigation of massive
star magnetism ever undertaken. In this paper, the first in a series reporting
the general results of the survey, we introduce the scientific motivation and
goals, describe the sample of targets, review the instrumentation and
observational techniques used, explain the exposure time calculation designed
to provide sensitivity to surface dipole fields above approximately 100 G,
discuss the polarimetric performance, stability and uncertainty of the
instrumentation, and summarize the previous and forthcoming publications.
