Volcanic ash soils result from the in situ weathering of volcanic ashes. These soils exhibit a distinctive behavior that is a consequence of its formation history, current mineralogy and structure. In this study, we analyze the formation history of Colombian volcanic ash soils to explain salient characteristics and develop an experimental program to explore thermal, electrical, mechanical and chemical properties in view of engineering needs. The mineralogical composition of volcanic ash soils is characterized by the presence of clay minerals that are uncommon in soils of sedimentary origin such as allophane, imogolite and halloysite. Dissolution and reprecipitation into new minerals has been accompanied by a large increase in porosity and the development of intercrystal bonding. High porosity and inherent cementation determine the strength, compressibility and conduction properties of these soils. In particular, Colombian volcanic ash soils exhibit a dramatic change in stress-strain response upon remolding. Consequently, the interpretation of field observations and laboratory test results, as well as the selection of construction operations must be carefully considered within the context of the formation history of Colombian volcanic ash soils.