Reg 883/2004 and 987/2009 modernized EU social security coordination by simplifying some rules while improving citizens' rights. Key changes included replacing regulations 1408/71 and 574/72, extending personal scope, and strengthening cooperation between institutions. While some simplification occurred, complexity remained in areas like applicable legislation and pension coordination. The new system preserved the general rules around social security coordination that had developed over 50 years of case law interpretations.