Thesis: Ph. D., Massachusetts Institute of Technology, Department of Economics, 2017.Cataloged from PDF version of thesis.Includes bibliographical references.This thesis consists of three chapters on information transmission and utilization in marketplaces and their implications on firm competition and quality discovery. The first chapter analyzes the dynamic effect of sponsored search advertising on quality discovery on the Taobao.com retail platform. In a stylized model, a new product's boosted exposure from sponsored search ads could help the platform to infer how well the product converts exposure to sales (the quality measure) and award top organic search ranks accordingly. Hence, sellers with higher private quality signals would bid m...