For those new to this topic who are seeking an easy-to-read introduction, there are two must-have books: True Selves: Understanding Transsexualism-For Families, Friends, Coworkers, and Helping Professionals, and Transsexual Workers: An Employer's Guide.
The first, True Selves, is a general introduction to the topic from a psychological point of view. It's written by two psychologists who are well-versed in gender issues. They detail the process of transition between genders, starting with legal and identity changes and proceeding to changing outward modes of self-presentation, including sample "coming-out" letters to employers and coworkers and dealing with bathroom issues, hormone treatments, surgical options, and guidelines for finding social support. First-person accounts from transsexuals augment general readability and put human faces on the issues discussed.
The second, Transsexual Workers: An Employer's Guide, also gives basic information about transsexualism from a therapeutic point of view, but also tries to specifically address the issues faced by HR and Diversity professionals. It gives some information on relevant civil rights and disability laws, tips for managing difficult situations, and a glossary. There are suggestions for dealing with coworkers' concerns, uncomfortable clients, the general public, and the media. Common workplace issues, such as pronoun usage, dress codes, restroom use, employee transfers, and health insurance, are addressed. A resource section lists helpful websites, national and regional organizations, books, magazines, and videos.
Some of you may wonder why these books use the term "transsexual," rather than transgender, and what the difference is. In a nutshell, "transsexual" is an older term used mostly in medical and therapeutic circles. It can be confusing, because some use it to refer only to those who have completed sex reassignment surgery, whereas others have different definitions. By contrast, "transgender" is a more expansive term that includes all those whose gender varies from traditional norms. Most HR and Diversity professionals use the term "transgender."