The following is a broad overview of the two primary methods for making homemade soap.  There are several variations on these two basic methods.

Many more details can be found by following the links provided below the overview of each method below.

Cold Process Soap Making (CP)

This process involves combining natural oils, lye and water.  The natural oils might include such oils as coconut, palm, olive and shea butter.  The oils are placed into a large stainless steel or enamel stockpot.  A solution of lye and water is made and added to the natural oils.  After the lye and water solution is added to the oils the mixture is stirred until it has a consistency similar to pancake batter or thin pudding.  The mixture is poured into either several individual soap molds or a larger mold that is later cut into individual soap bars.  Typically the soap is allowed to harden overnight and then taken out of the mold.  After a curing time the soap is ready to use.

CP soap easily pours into soap molds. It takes an hour or two to make and will harden overnight. The typical curing time is 2-4 weeks.  The texture of CP soap is very smooth or fine and for this purpose those who sell their soap tend to use this process.  Typically only 95% of the oils are converted into soap. The other 5% of the oils remain in the soap to add to the excellent skin conditioning qualities of homemade soap.

Details about making CP soap can be found at the following sites:

Miller Soap  Aqua Sapone  Teach Soap  About  Snowdrift Farm

Hot Process Soap Making (HP)

The process for HP soap is like the CP process up to the point where the mixture has a consistency similar to pancake batter or thin pudding.  At that point the mixture is cooked for a couple hours by gentle heat in a double boiler arrangement, a crock pot or in the oven.  After the soap has cooked it has a consistency like petroleum jelly but maybe a bit thicker.  When it cools down it hardens and can be used immediately without curing.

HP soap is more difficult to put into molds because of it's heavier consistency.  The additional cook time is about 1.5 - 2 hours.  The texture of HP soap is not quite as fine or smooth as soap made by the CP method, but it is still smooth.  In addition to being able to use the soap right away, the primary advantage of HP soap is that after the soap is fully cooked, specific skin conditioning oils or fats can be added.

Details about making HP soap can be found at the following sites:

Teach Soap  Teach Soap(Oven HP)  Aqua Sapone  Diane's Naturally