What are the various forms of contraception

There are various forms of contraception, ranging from natural family planning methods which are least invasive, to intrauterine devices which require a doctor's intervention:

(a) Natural family planning methods:
These methods are based on the principle that conception can be avoided by abstaining from sex during the woman's most fertile period.  The two most popular methods are the temperature method and the rhythm method.  These have a very high success rate when combined with other forms of contraception.

(b) Artificial barriers:
These methods mechanically block the sperm from entering the uterus.  These include condoms, diaphragms (soft rubber cup-like devices used with sperm-killing cream, inserted into the woman's vagina before intercourse), intrauterine devices or IUDs (inserted into the woman's vagina and kept there for the entire time she does not wish to conceive), vaginal insert contraceptives, etc. In addition to contraception, the advantage of these barrier methods is that they prevent the spread of AIDS and other sexually transmitted diseases. 

(c) Spermicides:
Creams, foams, jelly and similar substances with special spermicidal chemicals can be useful contraceptives.  These substances are inserted into the vagina before intercourse, and essentially immobilize the sperms and make them ineffective. 

(d) Birth control pills:
Birth control pills are specially designed to control the hormone levels of the woman.  These pills need to be taken daily, for the entire duration that the woman is sexually active and does not wish to conceive.  If taken correctly, success rate is close to 100%, but the drawback is that one needs to remember to take it daily, else it loses its effectiveness.
 

How effective are these various contraceptive methods

The table below indicates that the success rates are higher for contraceptives that are more invasive: