On-site building in architectural concrete is drawing increasing attention from architects because this plastic material provides greater freedom for creative design. It is possible either to select from a growing number of designs and surface textures or to devise new ones. Variations in concrete mix proportioning offer endless opportunities. The effects of special aggregates and sands selected for color have increasing appeal for cast-on-site work. Subtle rather than strong colors are usually preferred, and white cement is growing in popularity for selected parts of a building. The architects' concept of architectural concrete and the way they adapt it depends on their approach to the design and use of materials. Among the five architectural firms polled, three characteristic approaches have been identified. Each of these affects the extent to which the architect will use architectural concrete, the amount of ingenuity they will introduce, and how carefully and precisely they will expect the work to be done. The first approach is one of considerable flexibility whereby the architect is willing to adopt any creative technique or design needed if it is feasible. Often concrete is made to contrast strongly with other materials. Concrete shapes and edges must be precise and uniform. A second approach might be considered one of restrained use of architectural concrete in which innovative techniques are used only when there are few unknowns for the contractor. In this way a good result is more readily assured with less special effort and less conferring than otherwise between architect and contractor. This approach seeks to produce good, economical yet creative design. In the third approach bold geometric shapes produce a visual importance which minimizes the aesthetics of surface textures or even color. The shapes may derive from articulation of the spaces enclosed by the concrete shell or may truly be engineered developments of shell structures. Other shapes may derive from unusual spaces or the development of light-shadow forms such as window mullions or sunlight control devices.