The "Blue Books" are Missouri's Official State Manual, which since 1878 has been printed every other year. 1889-1972 are currently online, and searchable, with the rest to come.
It lists government officials, election results and various other facts and figures about the state.My first thought was that I don't have any Missouri government officials in my family tree, so I likely wouldn't find anything, but still...I knew well enough to at least plug in a few surnames and see what turned up.
However, while my mind was thinking about major government officials, they appear to list many elective and appointive positions by municipality in each edition. I do have one cousin who was either an Assistant City Attorney, or City Attorney in Maplewood, Missouri from 1961-1966, so his name appeared in three different editions. This didn't surprise me much.
I have another cousin who was employed by the St. Louis State Hospital as a Pyscho-Analyst/Lecturer 1959-1960, 1963-1964 and by the Missouri Dept of Public Health and Welfare in the same position 1961-1962. This also wasn't a surprise.
However, I learned a third cousin ran for State Representative from the 4th District in 1932. (They didn't win, but they did get over 5,000 votes.) [Third name down in image below. It only identifies initials, but if the initials are correct, I believe I know who they are. If the initials are incorrect, there are a few more options. The provision of the address should help me confirm my suspicions in a city directory.]
In addition to the complete Blue Books, Missouri Digital Heritage also now has a separate Historic "Blue Book" Photograph Collection
The Historic "Blue Book" Photograph Collection is a compilation of images considered for, or published in, the Official Manual of the State of Missouri. Just as the Manual is an important source of information about Missouri’s state government, history, and culture, these pictures capture the many facets of Missouri institutions, landscapes, and places. The images in this collection cover a wide range of subjects, including historic buildings and sites, college and university buildings, parks, bridges, and state government buildings.Here's one of the photographs:
It's Brookings Hall at Washington University in St. Louis. I, and several relatives graduated from the university, and I grew up only a few blocks away, so it's not an unfamiliar sight to me. However, the photograph was taken in 1948.