|Circulating tumor DNA (ctDNA) has been shown as a promising biomarker for monitoring several tumor types. We want to study the use of ctDNA in monitoring multiple myeloma, by use of digital droplet PCR (ddPCR). The objective of this thesis, was to perform optimization and validation of 14 ddPCR assays for further use in the main project on monitoring multiple myeloma with cfDNA. We found all assays to be highly sensitive and specific, with a false positive rate and limit of detection fluctuating between ~0.00 and 0,07 copies/uL of reaction volume, and with a linearity displaying a good dynamic range. The assays were used in our main project which culminated in a paper published in the journal Haematologica.