These notes on Modular Coordination in the Buildable Design Appraisal System are produced as part of BCA's Buildability Series. Its objective is to introduce designers to the concept of modular coordination and its benefits. At the same time, it gives some practical advice on the application of modular coordination using actual projects as examples. The recommended modules in these notes take into consideration the need for flexibility in design and the sub-module has been introduced for this purpose. As modular coordination becomes more widely practised in the local industry, these notes may be revised and the recommendations will be reviewed to achieve a higher level of modular coordination that will benefit the building industry.