Harlequin, Mills & Boon and Silhouette

As it is the centenary year for Mills & Boon, some people are wondering -- okay where does this fit in with Harlequin, and how did the two companies get together? And why for example are there three editiorial offices?

Harlequin was founded in 1949 in Winnipeg Canada to take advantage of the burgeoning paperback or pulp trade. Richard Bonnycastle was the mover and shaker behind the idea. And it was mainly to the presses rolling that he suggested it. His wife Mary was their first editor, proofreading the books at home. The Bonnycastles romance, in particular their wedding could have come straight from a Harlequin btw. Bonnycastle was at one time a fur trader and explorer and barely made his wedding.
The first book published by Harlequin was The Manetee. In the early days, they published all types of pulp fiction, generally they acquired rights to books published elsewhere in the world, but they did publish a few original works. In the early 50s, they discovered the medical romances from British firm Mills & Boon were proving exceptionally popular and they acquired more. In 1964, Harlequin start to publish romance exclusively, again mostly acquiring the rights from British firm, Mills & Boon. Then in 1972, they purchased Mills & Boon from the Boon family and the companies were joined.
Because Mills & Boon is such an iconic name in parts of the world, Harlequin kept the Mills & Boon name. They also kept the editorial office in London because it had served them well. (It continues to do so.)
In the late seventies, Simon & Schuster founded the Silhouette imprint to provide direct competition to Harlequin. Harlequin purchased Silhouette in 1984, after it received clearance from the US Justice Department. Silhouette's editorial office was based in New York and Harlequin continued to keep that editorial office there.
Hopefully, this goes some way towards explaining the how and whys Harlequin came about. And the various editorial offices are where they are.
If you want to learn more about the history of Harlequin, you can do so here.