Let's start with a definition of calisthenics. Wikipedia defines it as

"a type of exercise consisting of a variety of simple movements usually performed without weights or other equipment that are intended to increase body strength and flexibility using the weight of one's own body for resistance."

These are really simple exercises you can do most anywhere and with little or no special equipment. Ideally you would create a routine where you do a set number of each exercise a couple days a week. Over time you can increase your number of repetitions as you strength increases. How about a quick rundown of the most popular ones?

Sit-ups/Abdominal Crunches - While you may not end up with a washboard stomach, you can do some things to get your abdomen in better shape. Sit-ups and crunches have long been a favorite for many athletes for the very reason that they work. Lying on your back with knees bent, keeping feet flat on the floor, cross your hands across your chest and then curl your torso, rolling from your sternum toward your hips. Do this slowly and start out with a set of ten crunches in three reps. In other words, do ten crunches, wait a minute, do ten more, wait a minute, and then do the final ten. As you get accustomed to these, you can increase both the number of sets and reps.

Squats - Squats are excellent for gluts, hamstrings, quads, and calves. Although the official description says using your own weight, this is a good candidate for additional weight. Even if you just grab a couple of cans of soup. With your feet standing firm and spread apart about two feet, bend your knees slightly. Then, very smoothly, you will squat toward the floor without going all the way down.

Push-ups - Great way to use your own weight to work on your arms. While lying prone on the floor with your hands spaced evenly with the shoulders, press upward. Men should pivot on your toes keeping the length of your body straight. Women should pivot on their knees keeping the remainder of the body straight. Fully extend the arms, and then slowly return to the starting position.

Triceps Press - Having firm arms is something that many people focus on when exercising. The triceps are the other major muscle group in the arm and will help further define the upper arm. For an Overhead Triceps Press, standing on the floor with your feet about two feet apart, knees slightly bent, you will extend your arms over your head. Keep your elbows locked and then very slowly lower your hands behind your head. You want to do this with some type of weight, but small weights like one to five pounds. If you do not have weights of your own, you can hold a one-pound of vegetables, which will work perfectly.

In the end it is up to you to determine which areas you need to work on and which exercise best fits your interest and schedule. A final reminder, before starting any diet or exercise program consult with your physician to determine what is right for you. Good luck and good health.