The Price-to-Book (P/B) ratio is a financial metric used to compare a company's market value to its book value. It is calculated by dividing the current share price by the book value per share. A P/B ratio less than 1 may indicate that a stock is undervalued, while a ratio above 1 suggests it may be overvalued. Investors often use the P/B ratio to assess the value of companies, especially in sectors like finance and real estate, where assets are more tangible. It helps in identifying potential investment opportunities by highlighting discrepancies between market perception and actual asset value.