Dear Anonymous,This is a not infrequently asked question. The worry that your manuscripts need protection is pretty unnecessary, but let's go through this once anyway.
How safe is it to pitch a book idea?
I'm writing a book but don't want anyone to rip off my idea.
I don't send out stories, but if I did: copyright is more trouble than it's worth, and I've heard that the ways of documenting your manuscript via mail are not terribly secure in the legal sense.
This is where your critique group comes in handy. If you have been using a critique group, as you should, you have witnesses. But this is just a safeguard for worriers.
Let me be clear. The chances of your manuscript being stolen while at any of the reputable publishing houses are essentially the same as the chances you'll be killed by a python while riding a streetcar.
...But perhaps you're afraid someone will steal your idea. This is the concern that makes people at publishing houses laugh their espresso out of their noses. Your undeveloped, unrealized idea is intellectual property? Ah, the irony.
In publishing, execution is everything. Say, in 1998, somebody had come to me with the idea for a book about a kid who finds out he's magical and has to go away to school to learn about magic. My response would have been somewhere between "Eh," and "It's been done." Because it had been done. It took JK Rowling to express that idea in a way that was really what the market wanted. Behold the difference between idea and execution.
Ideas are not only a dime a dozen, they're recycled at a rate too fast to track. Write badly, and it doesn't matter how brilliant and original your idea is. Write well, and it doesn't matter how many times before your idea has been done.