The present design rules for fillet welds in Eurocode 3 lead to very thick fillet welds for higher strength steels S420, S460 and S690. Other design rules, e.g. the AISC specification [6] and the Canadian standard CSA-S16-09 [8] give much smaller fillet weld sizes for these steel grades. Another important difference is that the strength of the filler metal is directly taken into account in the design equation, while in Eurocode 3 Part 1-8 (EN1993-1-8, [3]) the strength of the filler metal is indirectly taken into account. EN1993-1-8 prescribes matching weld metal, while many other codes also allow undermatching weld metal for fillet welds. Allowing undermatching weld metal for fillet welds enables the designer to choose an optimal combination of parent metal, filler metal and welding parameters to comply with the requirements for ductility and strength. A summary is given of previous and present design rules and the results of recent research. Proposals for modification of the Eurocode 3 design rules for fillet welded joints are included, focussing on high strength steel.