Alternative splicing is a fundamental gene regulatory process producing distinct functional RNA transcripts. Splicing exhibits remarkable variability between cells and tissues. Tissue-specific splicing differences are abundant between human tissues. Genetic variation can affect tissue-specific splicing differences, but very little is known about the genomic determinants of tissue-specific splicing variation. We address this knowledge gap by directly mapping the variation in the differential splice-site usage between tissues by Genome-Wide Association Studies (GWAS). We combine the power of GWAS with SpliSER (Splice-site Strength Estimate from RNA-Seq), a tool developed by us that provides quantitative estimations of splice-site usage. By comparing the usage of the same splice site in different tissues, one can obtain a quantitative estimate of tissue-specific splicing differences. Through a comparative analysis of hundreds of shared splice sites across different tissues, we have identified genetic variations with tissue-specific impacts on splicing across hundreds of splice sites in the human genome. Our work significantly enhances our understanding of the genetic regulation of splicing across diverse tissue types. We will present the latest findings from our research, shedding light on these essential mechanisms and providing valuable insights into the world of tissue-specific splicing.