Cryptocurrency assets' integration into conventional portfolio theory is one of the most significant developments in modern finance. This comprehensive review addresses the evolving relationship between cryptocurrency markets and conventional portfolio optimization frameworks, taking into account how digital assets enhance and replace traditional investment strategies. Drawing from 18 peer-reviewed papers and institutional studies, this paper summarizes recent studies on cryptocurrency portfolio optimization, diversification benefits, and institutional adoption patterns. The facts confirm that even though digital assets offer unique diversification opportunities, their introduction requires radical transformations in the classical portfolio theory frameworks, particularly in the area of risk modeling and correlation behavior. The review contends that growing institutional adoption of digital assets requires an outright reinvention of portfolio construction methods for the digital age.