Is There a Happy Ending?
What do you do if your neighbor's large trees, within a few feet of the property line, are overhanging your yard?
Enjoy the shade, I'd say; but life is rarely that simple. The actual answer - as far as I have been able to determine from a good four hours' online research today - is that you are entitled to cut back the overhanging limbs, at your own expense, because your property line extends from the center of the Earth into the most infinite reaches of space. (No charging tolls on passing airplanes / satellites / asteroids / alien spaceships / comets / the incalculable array of matter floating through the boundless unknown! I mean, let's be reasonable here.)
But if you cut back the limbs (this also applies to encroaching roots, which are trickier) so severely that it damages or kills the neighbor's tree, your neighbor can sue you for damages.
If your neighbor is behaving in good faith, he may (but is not necessarily obligated to - this is a matter for local jurisdiction or civil action) pay for the trimming, or assist with payment. The neighbor may be motivated to do so because it ensures he has a say in how, exactly, the trimming is performed. You may (as long as it doesn't kill the tree) cut the limbs right back to the property line; imagine a laser beam, one poster remarked, raking straight up from the fence to the sky. If the neighbor finds this aesthetically or otherwise objectionable, it's certainly in his interest to work with you.
If your neighbor's tree drops limbs onto your roof or cars and causes damage, this is actually (unless the neighbor knew the tree to be unhealthy, and therefore predisposed to socially unacceptable behavior) an Act of God - or even, if you've failed to trim back the limbs that overhang your property - a result of your own negligence. You can file a claim with your homeowner's insurance, or sue God for damages. Either course is likely to be equally effective.
Excessive brush due to the incursion of overhanging limbs, and the wildlife dwelling therein, is definitely your own problem.
Do you know, I've worked on this issue, doing the best research I could, for about 8 hours so far. I asked a coworker for help with city ordinances in the jurisdiction in question, and he came back with detailed instructions on how to open a massage parlor.
Then my boss set me to 10-keying travel and tourism stats from the 50's. This is a day in my life. I can't figure out if I'm under- or overpaid. At least I don't have to trim trees.