This book introduces a new concept of profitability, called the 'efficiency rate of profit', which is defined as the ratio between the unit net margin and the unit capital requirement and shows how the efficiency rate of profit may be used in the assessment of mechanization and economies of scale. The book also shows how the efficiency rate of profit relates to the financial opportunity cost of investment, thus resolving the long-standing controversy over 'interest as a cost'. Using real-world plant-level data, the book explains fully the process of mechanization, how increasing returns to scale works at the plant level through power rule relating plant or equipment cost to capacity and how and why it is more cost effective to combine mechanization with expanding the scale of production in one combined 'package' of efficiency improvement.