There are as many versions of jerk seasoning as there are jerks. Central to them all is allspice, cinammon, nutmeg and Scotch Bonnet peppers (read habanero - the worlds hottest) then the food is cooked over pimiento wood.

The basic seasonings are usually made up into a jerk paste added to whatever other seasonings you might use. A simple jerk recipe is:

    1 C. olive oil
    1 finely chopped onion
    1 bunch chopped scallions(green onions)
    1/4 C. soy sauce
    4 cloves crushed garlic
    1/2 C. chopped parsley
    1/4 C. ground allspice
    2 T. fresh thyme leaves
    2 Scotch Bonnet peppers (seeded
      and chopped) wear gloves
    1 t. black pepper
    1 t. cinnamon
    Ingredients
    1/2 t. ground nutmeg
    salt to taste - depends upon how salty
       the soy sauce is.

Add a couple of tablespoons of this to whatever other seasonings you want to put on the chicken.