Technical Abstract: Soil penetrometers are useful tools that measure the penetrability, or strength, of a soil. They can be as simple as a rod or shaft with a blunt or sharp end, or complicated mechanically driven instruments with digital data collection systems. Regardless of their design, soil penetrometers measure soil penetrability and can detect differences in soil strength within a soil profile. Traditionally, penetrometers in agriculture have been used to detect soil compaction issues and depth to compacted soil layers. However, with advances in electronics and computing power, several researchers have created innovative uses for soil penetrometers such as the development of pedotransfer functions and 3-D mapping of soil landscapes from cone index data. With the advent of new technologies and coupling of other sensors, soil penetrometers will continue to be important useful tools in agrophysics.