A literature review was conducted to determine the factors affecting porosity in welds deposited by GTAW and GMAW. Hydrogen is the dominant cause of porosity in aluminum alloy welds.The sources of hydrogen most commonly encountered in commercial welding practice are hydrocarbons (grease, oils, etc.) and moisture contaminants on surfaces of the filler metal and plate. These contaminants are immediately converted to atomic hydrogen by the arc and are subsequently transferred into the molten weld pool in accordance with Sieverts Law.Although both primary porosity (forming from the liquid) and secondary porosity (precipitating from the solid) may occur in welds, only the more voluminous primary porosity is extensively covered in this review.