The Zombie Stack Exchanges That Just Won't Die
In many cases, libraries are the only institutions left that the homeless have access to, but on the other hand, other people might not like it. So how do libraries approach this challenge?
InquilineKea
It comes down to the individual library's policy.
When it concerns public libraries, which is where the homeless population issue seems to be primarily focused, it is normally in bad form to say that they are not allowed in the library. A public library is meant to be open and accessible to all members of the community, including the homeless. In many communities, the public library is the only place where there are resources available to help them. Many libraries will have policies in place that say there is no sleeping allowed, no large bags, or patrons must be using library materials while in the library. Policies like these discourage "hanging out", which is what many people dislike about the homeless in the library.
I know from personal experience, there are a number of homeless community members that spend a lot of their day in the library. If they are quiet, respectful, and following our policies, we don't bother them. If there are complaints from other patrons or they start becoming disrespectful to staff or the library then we address it. We request they calm down and stop their offensive behavior. If they do not, then we ask them to leave.
Our library has compiled some pamphlets with lists of local resources for the Homeless, from shelters to food banks, and more. Getting this kind of information to them can be especially useful in the winter.
Other than that, what is outlined in @KatieR's answer is good. Many may not know where else to go, or even if there are resources available to them. The library is probably the best place, if not the only one, where they can get access to that kind of information.
We have a more unique problem at the academic library where I work. The issue isn't with homeless exactly but through-hikers on the Appalachian Trail. We are close enough to the trail that they like to come and check their e-mail (not a problem), catch up on the newspaper (not a problem) and bathe in our bathrooms (problem!). It's not only the that bathing at a sink is in appropriate, it's the abuse of paper towels, soap and the mess left behind in the sink (shaving) and water on the floor. It's difficult to know when a hiker is misusing the facilities without going to check, which seems awfully nosey.
Another aspect to consider is having clear policies. Many libraries have been sued over anti-homeless policies because they were not followed consistently. If there is something about smell, do you kick out anyone who has an offensive smell, like too much perfume? If you say no big bags, do you go after the student with a big bag as well as the homeless? There has to be consistent enforcement.
One of the most famous examples is Kreimer v. Morristown (which goes all the way back to 1991) http://www.ahcuah.com/lawsuit/federal/kreimer1.htm
Public libraries that are open and welcome to all should have good behavior policies that are followed equally by all staff. If your library has identified behaviors that are problems the transient community has exhibited, include them if they are things you would expect to have followed by all visitors.
For example, my library includes:
Those two rules take care of most of the problem issues we see exhibited, and they are rules we enforce with any visitor breaking them.
It's separating the behavior from the person that is most important to keep in mind.
Require log-ins and time limits on all computers. Add sleeping and legal B.O. policies to the code of conduct. If you are lucky enough to have security, have them check the bathrooms regularly. Also, invest in a good ventilation system, or air freshener.
This discussion isn't the time to show everyone how liberal you are. The homeless need social services, not libraries.