Since 1980, partnerships' and S corporations' share of business receipts increased greatly. These entities generally do not pay income taxes. Instead, income or losses (hundreds of billions of dollars annually) flow through to partners and shareholders to include on their income tax returns. GAO has previously reported that the misreporting of income by partners and shareholders poses a tax compliance risk. This book describes what is known about misreporting of flow-through income; assesses how much misreporting IRS identifies; and analyzes possible improvements in IRS's use of data to better identify partnerships and S corporations to consider examining. This book also analyzes individual tax return data to determine who earns pass-through business income and bears the burden of taxes on that income.