I thought I already mentioned this recently but apparently never did, but it's worth a mention:
A Selective History of Part 15 of the FCC Rules: An Engineering Perspective
By Daniel Hoolihan
Published August 1, 2025
I think the whole thing is an interesting read -- but to get right to it, you may want to skip the first section and scroll down till you get to to the heading: "Part 15 First Appears – 1938" and the read on from there. It's a good overview.
I thought I had already posted the above link before. I just happened across the page again and gave it a re-read. This Compliance Magazine article is definitely one of the better articles that summarize part 15 history (although I could nitpick at a couple things it says). Its really a great read, I encourage you to check it out, but as a teaser, below is a heavily truncated version of it:
A Selective History of Part 15 of the FCC Rules: An Engineering Perspective https://incompliancemag.com/a-selective-history-of-part-15-of-the-fcc-rules-an-engineering-perspective
"... In 1938, we see the first mention of low-power devices in Part 15 of the FCC Rules ... adopted in November 1938 and remained in effect for low-power communication devices until 1957. ... After World War II, low-power radio devices increased rapidly, ... to use frequencies that were higher than the AM broadcast band. To address these new issues, the FCC .. in April 1949 ... an overall revision of Part 15. It wasn’t until April 1954 ... low-power devices were divided into two categories: .... A second report and order in Docket No. 9288 was issued in 1956 and 1957. ..
With respect to Part 15, the 1970s will be known for ... the FCC adopted new rules on digital electronic equipment (especially computers) ... the FCC in March 1980 made a few minor changes .... Another major impact of FCC Part 15 devices on society started in .. 1998 ... signaled the implementation of what were called Telecom Certification Bodies (TCBs), beginning in June 2000. .... In its FCC ET Docket No. 99-231 – ... the FCC amended Part 15 of its rules relative to spread spectrum devices. The rapid expansion of wireless devices .... The FCC, as a single source of testing, would not have been able to test all the new product designs released as a result of the wireless demand. However, industry responded with additional testing labs ...
Part 15 – Low Power Devices continues to be an important part of the FCC Rules. Many clever innovations have resulted from the category of “unlicensed” products unleashed on society ..."