Digital platforms have fundamentally transformed economic interactions by reducing transaction costs, facilitating information exchange, and shaping market structures. These platforms rely on algorithms, reputation systems, and pricing mechanisms to create efficient marketplaces. However, the design choices of these platforms - such as rating granularity, pricing strategies, and algorithmic personalization - can have profound implications for fairness, efficiency, and long-term market outcomes. At the same time, the rapid digitization of commerce has altered the dynamics of online and offline interactions. While digital platforms provide opportunities for businesses to expand their reach, they also introduce challenges related to market cannibalization and algorithmic dependence. This dissertation examines platform design and the impact of digitization in digital markets.In Chapter 2, I study rating granularity on online platforms by developing a dynamic model that reveals a fairness-efficiency trade-off. Coarser ratings support new entrants but lead to information loss, and I identify an optimal granularity level that maximizes platform revenue. Chapter 3 explores price signaling in service platforms, where I provide empirical evidence that high-quality firms use low introductory prices to build reputation, highlighting the role of pricing in quality discovery. Chapter 4 investigates algorithmic dependence in personalized recommendation systems, demonstrating that while personalization enhances short-term user welfare, it hinders long-term preference learning, with policy interventions proposed to balance these effects. Chapter 5 analyzes the impact of online store openings on brick-and-mortar businesses, showing that product categories react differently to digital expansion, offering new insights into the dynamics of omnichannel retail and providing actionable guidance for adapting mall strategy in the digital era. This dissertation contributes to platform economics, algorithmic personalization, and digital commerce by providing theoretical insights and empirical evidence to guide platform design and business strategy.