In this review we discuss a wide range of alternative approaches to the reduction of CO2 emissions associated with the manufacture of the binder phase in concrete.They are classified broadly as follows:(1)Use alternative fuels and/or alternative raw materials in the manufacture of Portland-based cements.(2)Replace Portland clinker with "low-carbon" supplementary cementitious materials (SCMs) in concrete.(3)Develop alternative low-carbon binders not based on Portland clinkers.The first approach mainly represents incremental improvements that can be achieved fairly easily and cheaply as long as suitable raw materials can be found.The second approach ranges from incremental improvements, if low levels of SCM substitution are used, all the way to major innovations for binders with very high Portland clinker replacement levels.The third approach is the most risky but also holds the greatest promise for truly significant CO2 reductions if it can be implemented on a large scale.