UPDATE: As of July 2022 they are closed to unsolicited submissions. It is not clear if they plan to reopen.
Workman Publishing is a large independent publishing company that now includes a number of separate imprints (most started out as their own companies and were purchased by Workman). The imprints include large established companies like Algonquin Books (which is no longer open to un-aganted submissions). The original Workman imprint is open to un-agented submissions. They focus on publishing exclusively nonfiction books for children and adults, as well as calendars. They do not accept unsolicited picture book submissions.
To get a good idea about what the Workman imprint publishes, visit their page here. They have good distribution and I recognized a number of their covers from the display case at my local bookstore, which is always a good sign. Some of the famous books they have published in the past (they have been around a long time) include The “What to Expect” series (best known for the Book What to Expect When you are Expecting).
They prefer to receive all submissions via email. Any hard copy submissions must be of copies. They do not want original work and will not return original work. Please specify if your book is for the Children’s department.
They have clear submission guidelines and the entire proposal should not be longer than 30 pages, this includes the first chapter. Read their submission guidelines carefully, because it is important to follow them.
They do respond to all submissions, but it generally takes them around 5 months. Please do not query them before that.
To learn more go to their submission page here. The submission guidelines for the Workman Imprint are up first on the page.