The　microstructural　characteristics　and　their　evolution　in　weld　metal　and　HAZ　(heat　affected　zone)　of　Aluminium　alloys　and　Titanium　alloys　were　presented　with　the　emphasis　focused　on　the　behaviour　and　influence　of　grain　growth,　texture　and　crystal　lattice　distortion.　The　influence　of　welding　processes　and　techniques　were　analyzed　based　on　the　changes　of　deformation　and　hardness　distribution　in　welded　joints.　The　fracture　mechanisms　were　evaluated　via　the　analysis　of　fracture　behavior　and　toughness　of　the　joints.　Life　estimation　methodology　for　welded　joints　and　structures　of　light　metals　were　discussed　within　the　framework　of　fatigue　failure　mechanism,　fatigue　strength　evaluation　and　fatigue　life　prediction.　Finally,　the　outstanding　scientific　problems　and　the　potential　solutions　were　discussed.