'Dynamic scoring' means taking full account of all the economic effects of policies when estimating their budgetary effects. Taxes and government spending have multifaceted economic effects. Individuals and firms may respond by changing their behaviour in innumerable ways, and these responses can themselves have further economic effects, by changing supply, demand and market prices for goods and services. Reforms may also prompt responses from other policy-makers. All of these affect the government's revenue and outgoings, so the full chain of consequences will determine the actual cost of tax and spending proposals. Incorporating these effects in the costing of policies is almost self-evidently attractive, but it is formidably difficult to achieve. This project assesses the key conceptual and practical challenges it poses and considers the pros and cons of incorporating economic effects in the scoring process.