Are you frustrated because your kids are grown up and old enough to be self-sufficient, yet they're still living with you? Is your home starting to feel like a free hotel? If you've decided it's time for one or more of your children to leave the nest, but they refuse to spread their wings, here's what to do.
Assess the situation as objectively as possible. As a parent, you might have mixed feelings about encouraging your child to move out. On one hand, you might enjoy the company, or you don't want him/her to struggle on his or her own, or you don't want to feel like you're "kicking" anyone out. On the other hand, perhaps you sense that your child is not pulling his/her own weight, and if you don't take action s/he might never become self-sufficient. It's important to sort through all of these feelings before you talk to your child.
Make a list of the reasons you want your child to move out. Be honest-- confront any ways in which having your child live at home makes you feel uncomfortable, and don't allow guilt to make you bite your tongue. Some reasons are obvious, such as if your child blatantly disrespects your privacy or belongings. Some reasons are subtle and somewhat personal and embarrassing, like overhearing your child with his/her lover(s), or the fact that you seem to be the one who ends up doing his/her laundry.
Consider whether there is a real reason your child cannot live on his/her own. Sometimes a parent is reluctant to push a child out of the house if they believe the child simply doesn't have the resources to live independently. In most cases, however, the child is perfectly capable of being independent, but it will require some downgrading -- like moving from a house to a barebones apartment with roommates. If you determine this is the case, recognize that by allowing your child to stay, you're catering to his/her comfort, not to real circumstances.
Show a united front. It's very common for one parent to want a child to move out and the other parent to be resistant to the idea. But before you can nudge your child towards independence, you've got to be on the same page. See How to Compromise With Your Spouse.
Ask your child if s/he wants to move out. This is a simple question, but will reveal a lot about why the child is still living at home. Usually the answer will be something like "Yeah, of course, but..." followed by a list of reasons why it just can't happen at the moment. Evaluate those reasons objectively, keeping in mind that there are probably other reasons --real reasons - that your child hasn't verbalized, such as that s/he enjoys having you to do his/her laundry, or being able to use your car without having to make car or insurance payments, etc. What you want to do is address the verbalized reasons (which, in many cases - but not all - are excuses) one by one, with facts:
"I'm looking for a job." Is that true, really? How often is s/he checking classifieds and job sites? In the meantime, is s/he volunteering so that s/he can make contacts, and can account for any gaps in his/her resume? Is s/he looking for "a" job or "the" (perfect) job? Is s/he unwilling to work a minimum wage job until s/he finds something better?
"I can't afford a place." Is it that your child can't afford a place, or that s/he can't afford a place as comfortable as your place? Maybe s/he can't afford a place in your neighborhood and there's a reason for that; living in a nice neighborhood is one of the rewards of having a successful career. Look around: Where do other young adults live? Does your child feel like s/he's "too good" to live there? Do you feel like s/he's "too good" to live there?
"I want to save up for a house, car, grad school, etc." This is probably the most legitimate reason to stick around at home, but only if your child is accountable to it. How much does s/he actually have saved up? What is the ultimate goal? Is s/he consistently putting money away, or do his/her savings patterns depend on how many good movies or video games are out that week? If s/he can prove that saving money is a priority for him/her, it's all good. But don't just take your kid's word for it. If that's the reason for staying home and getting a free ride, you're entitled to see pay stubs and bank statements, just like financial aid offices are entitled to see tax forms before they provide financial assistance.
Treat your child like a person renting a room. It may be hard to remember sometimes, but adult children living at home are still adults. A sure way to set yourself up for conflict is to over-parent your adult children (removing video game consoles, preventing them from having guests in their room, asking them to do chores). Adult children living at home who are over-parented and over-supervised will rebel as quickly as teenagers. Not only that, but by continuing to attempt to parent them as if they were still children, you are infantilizing them - they will not develop the skills needed in the outside world. So you need to develop some strategies to establish a new adult-to-adult relationship.  Step outside of your role as a parent and treat your child as if s/he were a stranger renting a room in your home. Not only will this make your child less comfortable with living in your home, but it will also prepare him/her for renting a room somewhere else.
Collect rent. Check the local classifieds to see what people are charging for rooms in your area. Set a monthly deadline and enforce it. If your child is late with payment, there will be a late fee. If the rent is not paid, you must firmly insist that the child may no longer live there.
Lay down rules about noise. Most apartments have "quiet times" that begin around 11pm and end around 7am. Make it very clear that you don't want to hear any noise from them during these times - no loud TV or music, no audible laughing, talking, or guests, etc. Lay out the consequences for "noise violations" such as more than 2 noise violations a month results in a rent hike.
Consider not providing meals. Would you feed and clean up after someone renting a room? Most people simply allow the renter access to their kitchen. The renter still has to buy and cook their own food. Your child may complain that s/he can't cook, or doesn't have time to cook, but many a young adult throughout modern civilization has gotten by on TV dinners and Ramen noodles for a few years in their lives. If you're concerned about nutrition, give your kid a bottle of multivitamins.
Set standards for cleanliness. Since this is an adult you're dealing with, let his/her room be a private domain. Generally, if you can't smell it from the hallway, it's none of your business. But, make it clear that s/he is responsible for cleaning after him/herself throughout the rest of the house - cleaning dishes, doing laundry, putting garbage in the garbage can, etc. This is a difficult standard to enforce, but there are ways. For example, if laundry or garbage is left laying around, pick it up and put it right in front of the kid's door, so that it builds up and makes it difficult for him/her to enter and exit the room.
Grant him/her some privacy. Do not go into that room unless the smell is unacceptable. If it's messy, shut the door and leave it be. That room belongs to another adult, and it's none of your business what's going on in there. If you're asking for rent and it's being paid, as long as reasonable quiet time and cleanliness rules are being followed, you really should not intrude. If you are granting the room, and your child is following your rules for living in your home, you should not be picking at him/her, and you should not be sticking your nose into his/her living space.
Be firm. This is the most difficult part. If you've done a comprehensive job of laying out the rules and specifying consequences, it's essential to follow through. You have to know under what circumstances you'd be ready to pack up your child's stuff, put it on the front lawn, hand him or her a list of local rooms for rent, and change the locks. If you can't imagine yourself doing this under any circumstances, you should accept that your child will live with you on his or her terms, not yours. And you might want to read How to Overcome Martyr Syndrome and How to Stop Being a People Pleaser.
Remember that sheltering your adult children from the harsh reality of life isn't helping him/her. Your job as a parent is to teach your children how to become independent adults who can survive and thrive on their own.  Your love and sympathy won't help them when you're gone. Remember the Chinese proverb: "Give a man a fish and you feed him for a day. Teach a man to fish and you feed him for a lifetime." And remember that, far from helping your child, you are robbing your child of the sense of pride and accomplishment s/he will get from navigating the difficulties of life without your help. Getting a job and living independent of you doesn't only benefit you - it benefits your kid. You can always lend a hand with a little extra cash, plus sympathy, love and understanding, if times get too rough and your kid cannot seem to keep his/her head above the water. But letting him/her struggle a bit is great for building character and helping him/her learn to be strong on his/her own.
Scrutinize your child's excuses, and understand his/her motivations. Instead of listening to what your child is saying, pay attention to his/her actions. There is the clarity. For example, your child may be arranging lots of job interviews, but not getting hired. What could be happening here is that setting up interviews may be the end goal to your child, because it keeps you satisfied. However, once there, s/he is not doing his/her very best at interviews because s/he doesn't feel pressured to actually get the job. S/he has the luxury of waiting for the "perfect" job opportunity to roll around, and that may never happen (or by the time it does, s/he'll have so little experience that s/he won't have a shot!).
You're not the only one struggling with these issues. Children who come back home as adults are called "mammoni", or "mama's boys" in Italy; "parasaito shinguru", or "parasite singles" in Japan; "boomerangs" or "twixters" in the US; "KIPPERS" (short for "kids in parents' pockets eroding retirement savings") in the UK; and "Hotel Mama" in Germany. There are parents across the world who will identify with your struggle to give tough love. Seek their support and advice.
If you can afford it, a very nice thing that some parents do is to collect rent from their adult children, take a small portion to help with household expenses, but put the great majority of the money in a special account. When the child either volunteers to move, or the parent asks him/her to move out, the parents present the adult child with the money stockpiled from rent payments. This helps with down payments/move-in fees like first and last month's rent, and the like. Generally this is most successful if the child has no idea that the parents plan to do this until the gift of the cash is presented. It's really best if the child believes that rent money is simply his/her obligation to pay and that you expect it on time each month - any landlord expects the same.
A more extreme measure is to move. Some parents retire to a more remote, relaxed location where their adult children won't have much fun, or where people under retiring age aren't allowed. You could also downsize your home, and explain to your child that you need to save money for retirement, that there's not enough room for them in the smaller home/apartment.
Before deciding to kick your adult children out of the house, listen to your adult children's point of view and let them know the reasons for your opinions. Real adults are willing to listen to other adults to solve problems. Perhaps you and your children can work something out.
On the other hand, remember that your home was bought with your efforts and your money. You are under no obligation to "work something out" with your adult children. If you simply want to enjoy your home without your children in it, that is your right, of course. It is simply suggested that all parties show some compassion to the others involved in the interest of maintaining a good family relationship.
If your child is stubborn and used to being babied, things will get worse before they get better.
Before going so far as to change locks, remove belongings, etc, understand your local laws regarding the eviction of tenants. Even though they are family and may not be paying rent, many places have eviction laws that may apply and must be followed.
Remember that the economy is very difficult right now. Jobs can be scarce and low paying, but housing and living expenses are high. Be reasonable in your expectations.
Be sure that your child is not suffering from some mental illness, such as depression. These illnesses can be debilitating. You may need to help them get them help. Although once a child reaches the age of majority (is no longer a minor), you have no obligation to him or her, denying that there is an actual illness working in this type of situation is irresponsible and potentially harmful to your child.