I have a very regular client, whom I adore, who enjoys pushing his envelope.  He likes me to come up with new ideas to explore his long-repressed sexuality.  He seems to be developing an interest in wearing women's clothing.  So far we have gone to Fredericks (I know, poor quality, but they have big sizes) and bought a variety of panties which I have him put underneath his pants when we go to dinner.  He wants to go more in that direction.  I don't have any understanding of what the turn on is: I have always turned down cross dressing clients because I just don't get it.  
I am asking for some guidance in exploring the psychology of this fetish so I can better serve my clients needs/curiosity.  Books?  Websites?  Academic studies?  Personal experience?
Thanks!  

xoClair

Glen or Glenda was the first film by notoriously bad film maker, but recently hailed counter-culture hero, Edward D Wood, Jr.  (He of Plan 9 From Outer Space fame)

As odd as this film is (And it is very odd even by Ed's own standards.) it gives a glimpse into the mind of the man who was the real deal.  The film purports to be a documentary but it quickly goes through the looking glass.  The producer thought he was getting a film about sex change operations.  He was not happy with the results.

Ed even wore women's panties under his battle fatigues when he fought in the Pacific in WWII.

There are at least four and probably more video documentaries about Ed's life and work, most of which highlight to some extent or another he=is transvestism.  The best is one called Look Back in Angora.  As far as biography goes, there is a film made by Tim Burton with Johnny Depp as Ed that is pretty faithful to the book it was based on and is quite entertaining.

I'm sure there are many psychological studies on the subject too.  

For myself, When I was a college student, I waiting one night for my date in the gal's dorm room, and she was very late; so as a gag, I undressed and donned her silky nightgown and got into her bed and waited for her there.  I was quite enamored of the feel of the apparel's material.  She seemed amused at first when she showed up, but we didn't end up dating very long, however.

Since then I've pretty much stuck to men's clothing, though I do wear men's silk briefs.

Cross-dressing is really specific from person to person.  Some of my clients love cross-dressing because they love and adore women and want to feel more feminine.  Some of my clients have "alter egos" that are feminine in nature.  Some of my clients really like gender-swapping.  The only play I don't do when it comes to cross-dressing is degradation or humiliation play concerning how embarrassing it is to look/dress like a woman.  

But really! you should ask him what attracts him to cross-dressing and go from there.  

A few great books are The Loving Dominant (this book is written from a male Dom/female sub perspective, but it's still great), The Mistress Manual is great and offers great scenarios, as well as The Sexually Dominant Woman: A Workbook for Nervous Beginners.  The book was really helpful to me when I first started dealing with cross-dressing.  

Hope this helps!

Great suggestion.  thanks!!

Ask him his girl name & start referring to her as that, then inquire about what lingerie she enjoys wearing that makes her feel sexy.  Communication is key, so ask the source.

I'll do my best to explain the turn-on . . .

If you accept the theory that every person has both female and male energy, then crossdressing can be a means for men to tap into their female side, see how the other half lives and what it's like to be a woman.  Men don't usually wear silk underwear, so panties feel fucking awesome rubbing up against your erect penis.  Crossdressing also has elements of the taboo, which, of course, makes it very exciting.  Modern women wear men's clothing, so it usually isn't as big of a deal for females to crossdress, unless they are doing the whole "drag king" thing, where they are actually "packing" a prosthetic penis and they have to go out into the world as masculine-presenting as possible (maybe even with fake facial hair, breasts taped down, etc.).

I think that you both need to ask yourselves what your intent is with either crossdressing or "forced" feminization roleplay and scenes (i.e., what are you trying to accomplish?).  Is this in the context of power exchange?  Are you trying to cause embarrassment/humiliation, or are you just facilitating making your client feel like the woman that (s)he always wanted to be?  Are you also incorporating age play (e.g., is your client a naughty little teenage slut) or sexy slut training (e.g., the French maid)?  Is the dress-up meant to be gentle ("sissy" play, with softer colors and lace), possibly with a maid/service aspect involved?

This is not universally true, but many men cannot emotionally/psychologically take anal play unless it's "not them" being penetrated, so "forced" (note the ironic use of quotes) feminization helps them get into a head-space where they can think of that part of their body in the context of a vagina to be  violated by a strap-on or other toys.

Amazon.com has a bunch of books on this subject.  I haven't read it, but The Lazy Crossdresser book has long been considered one of the best on this subject for newbies

Lots of info/food for thought.  
And the beat goes on...

xoClair

If he wants to explore being a woman, you could either train him to be a slut, or your perfect sissy maid. Either way, he's going to have to learn--
- how to walk in heels (and with those shoe bondage cuffs as well - the sub shop used to sell them, but I'm sure they're still available somewhere)
- to keep his posture straight and ladylike (we all remember carrying books on our heads for ballet practice, don't we? A posture collar will help an especially slouchy slut straighten up!)
- to purchase makeup, especially fun if you make him go with you to the makeup counter to get color matched!
- and of course, all the womanly wonders of how to seduce any man, and what to do with him when he's under your spell  

I'm not really so much into cross dressing in and of itself, but I am a devout lingerie fetishist so my, um, girls and I have something in common