This book covers the basic stories on allowances for doubtful accounts, including the approximate approaches on several estimations. Based on an academic structure, and publicly-traded firms, this book expects to show the simple insights on framework along with financial evidence toward the level of effectiveness of doubtful accounts. With the presence of other more technical books, at least, it is expected that this book is able to provide another angle of simple perspective on allowances for doubtful accounts and approximate estimations.