The properties of the solid-state of drug substances are critical factors that determine the choice of an appropriate salt form for the development of the pharmaceutical formulation. The most relevant properties may affect the therapeutic efficacy, toxicity, bioavailability, pharmaceutical processing and stability. The salt form must fulfil the needs of the targeted formulation, be suitable for full-scale production and its solid-state properties maintained batchwise as well as over time. Comparison of the solid-state properties of different salt candidates may be quite complicated if each salt candidate exist as different solid phases: polymorphs, solvates or amorphous forms. Thermal analysis, microcalorimetry and combined techniques, X-ray diffraction, solubility, intrinsic dissolution, sorption-desorption and stability studies are basic techniques for the characterisation of the salt candidates. Some examples show the role of the salt form as well as the polymorphic form in the characteristics of the solid-state. Thermal analysis and combined techniques are efficient for the detection of unexpected phase transitions and for the comparison of the suitability of the salt candidates prepared for salt selection.