Crypto currencies have rapidly gained popularity and adoption over the past decade. This conceptual paper provides an extensive literature review on crypto currencies, examining their growth, risk interdependence, volatility dynamics, and impact on fiat currencies. The review synthesizes key findings on the evolution of the crypto currency landscape, the interconnectedness of major crypto currencies, their asymmetric volatility patterns across timescales, and evidence of crypto currency returns Granger causing fiat currency returns. The conceptual analysis highlights research gaps and future directions for understanding crypto currency markets, risks, and integration with the broader financial system