The formation of open-mode discontinuities is a common occurrence in soils. This family of discontinuities includes hydraulic fractures, gas-driven fractures, desiccation cracks, ice and hydrate lenses, and even roots. These discontinuities can be analysed at the particle scale or at the macroscale using constitutive models that are consistent with the effective stress-dependent behaviour of soils. Both analyses show that the medium is in compression everywhere and that growth is intimately related to unloading and expansion ahead of the tip. While these observations appear to be common to the development of all open-mode fractures in soils, there are pronouncedinvasion differences between miscible fluids and immiscible phases.