INTRODUCTION: Fresh concrete properties are related to the properties of hardened concrete. Poor placement or consolidation leads to honeycombing@ which reduces compressive strength and increases permeability@ thereby leaving the concrete open to chemical attack. Nevertheless@ fresh concrete properties are not always properly measured or predicted. The main measurement of workability@ the slump test@ is not always applicable; at the same slump value@ two concretes may exhibit different work abilities. On the other hand@ hundreds of tests were designed over the years to measure the workability of concrete. The question is how to select the proper test for the application at hand and how to interpret the results obtained to predict the performance of the concrete in the field in the fresh state. To address these questions@ it is necessary first to define workability in terms of fundamental physical entities@ as described in the science of rheology. Therefore@ this report has four main parts: 1. Definitions related to rheology and workability; 2. Critical review of the tests available to measure the workability and rheological performance of fresh concrete; 3. Discussion of the factors affecting the performance of fresh concrete; and 4. Examples that illustrate the application of rheology and material science to predict or improve the performance of fresh concrete in the field. This report presents issues related to the design of a workable concrete for an application. Workable can mean no flow (zero-slump) or flow like a liquid (self-consolidating concrete [SCC])@ depending on the application.