Tony Thirlwall was a British economist who maintained that many of the insights of Keynes, especially with respect to the importance of both the level and the growth of aggregate demand, are still of great relevance today. He was particularly sceptical of the neoclassical approach to growth, developing an alternative theory that subsequently became known as Thirlwall’s law. This demonstrates the importance of the balance of payments in constraining the growth of output. Thirlwall also showed that the natural rate of growth could be affected by the pressure of demand. Thirlwall’s other major area of research was development economics, where he made many notable contributions, especially along Keynesian-Kaldorian lines.