Biomass is among the most promising renewable resources to provide a sustainable solution to meet the world's increasing usage of it in biochemical and thermochemical conversion technologies. Thermochemical conversion processes (pyrolysis, gasification, and combustion) thermally, convert biomass into energy-dense intermediates that can be, in turn, converted to power, liquid fuels, and chemicals. The performance of the processes and quality of the intermediates are strongly affected by endogenic and technogenic inorganics. This review highlights investigations on the effect and the fate of inorganics during pyrolysis, gasification, and: combustion of lignocellulosic biomass and critically and comprehensively presents pretreatment and post-treatment approaches for inorganic removal. During pyrolysis process, the inorganic contents can have significant catalytic effects and change the thermal degradation rate, chemical pathway, and bio-oil yield. During combustion process, the inorganic contents can bring various technological problems, environmental risks, and health concerns. During gasification process, the inorganic contents cause diversified downstream hazards. In recent years, several pre-treatment (mechanical, thermal, and chemical pre-treatment) and post-treatment (gas product and liquid product post-treatment) approaches have been employed to, control and diminish the impact of inorganics during thermochemical conversion. Effective pre-treatment technologies exist to remove inorganic contaminants to lower concentration limits. However, the main drawbacks of these pre-treatments are that they (i) reduce the overall efficiency due to the need of further drying process of wet biomass after pre-treatment and (ii) increase chemicals, facilities, and drying costs. Post-treatment technologies are utilized to meet the Strict levels of cleanup demands for the downstream applications. A great number of technologies exist to purify the raw synthesis gas stream that is produced by thermochemical conversion of biomass.