Host cell proteins (HCPs) are low-level, process-related protein impurities in drug products derived from the host organism during biotherapeutic manufacturing. During the expression of a recombinant protein drug, host cell systems can express many endogenous proteins. Purification of the drug from these HCP contaminants can be challenging, with low-level contamination remaining after purification. HCPs, accompanied by recombinant biotherapeutics, can significantly affect drug efficacy and cause immunogenicity. Detection and quantification of residual HCPs as potential process-related impurities is critical for biopharmaceutical companies per regulatory agency guidelines. In this ebook, we dive into some of the current challenges that biomanufacturers face when analyzing their production streams for impurities and what they are doing to improve detection methodologies for HCPs.