AbstractMIL‐STD‐781 specifies reliability acceptance test procedures based on both fixed‐length tests and probability ratio sequential tests. The assumption underlying MIL‐STD‐781 is a constant mean time between failures (MTBF) and typical practice applies MIL‐STD‐781 to electrical, electronic, and mechanical equipment. This article discusses some of the difficulties that have prompted the C and D revisions of MIL‐STD‐781. In addition, it discusses the relationship of MIL‐STD‐781 with MIL‐STD‐1635(EC) which deals with reliability growth testing. The article concludes with a discussion of needed research in reliability growth testing, in support of MIL‐STD‐781, and in the area of