Development of better, larger, and more dense focal plane arrays has stimulated the design of lens systems of larger aperture, longer focal lengths, and nearly diffraction limited performance over larger fields of view. As performance requirements, and the number of optical elements increase, the process of aligning lens elements during assembly rapidly becomes a critical issue. Tolerances on spacing, centration, and tilt become very challenging, as do the requirements on stability over extreme ambient excursions. This paper is intended to give a top level, general treatment of the subject, while describing certain techniques that incorporate precision alignment and measurement of critical lens parameters during assembly. These methods also allow monitoring during the accompanying bonding and curing cycles used throughout the build process. Examples serve to illustrate some of these techniques, and results are presented for specific cases. It is shown that centering, as evidenced by axial runout, can be set to the ten microinches level with a few microinches accuracy and maintained to about 50 microinches through the assembly and bonding process. With the use of computer data logging and analysis techniques, this can be extended to below five microinches.