Splicing and the S L 2 ( C ) SL_2({\mathbb C}) Casson invariant

We establish a formula for the SL2(C)SL_2({\mathbb C}) Casson invariant of spliced sums of homology spheres along knots. Along the way, we show that the SL2(C)SL_2({\mathbb C}) Casson invariant vanishes for spliced sums along knots in S3S^3.