Soldering joins two (or more) metals together using an additional metal (the solder - typically a lead/tin alloy). This method is normally used to join electrical connections. Brazing is similar to soldering except the additional metal us normally a harder alloy. This method is normally used when the joints need to be strong but the metals being jointed are either too delicate to weld or have a melting point that is too high to be welded safely (without compromising the object being welded). Welding joins two or more metals together by fusing them with a very high temperature. The following post on Yahoo provides a much better (and verbose) definition of the differences. https://answers.yahoo.com/question/index?qid=20080822064021AAGec8X