Ratio analysis measures relationships between financial variables to show how a firm's situation compares to its past, other firms, and the industry. Ratios are used to identify performance, standardize information, provide early warnings, and enable trend spotting. Key types of ratios include liquidity, activity, debt, and profitability. Liquidity ratios measure a firm's ability to pay obligations and include current, quick, and cash ratios. Activity ratios evaluate efficiency through measures like inventory turnover, accounts receivable period, and asset turnover.