Anaerobic digestion (AD) is a biotechnological process in which organic matter is microbially converted into biogas and digestate. Many parameters affect the underlying microbial processes, including depolymerization of organic compounds, acidogenesis, acetogenesis and methanogenesis, as part of the AD cycle. Optimal concentrations of different nutrients and micronutrients are a prerequisite for optimum microbial growth and metabolism in AD processes. The effluent digestate can be used as a substitute for chemical fertilizers, recycling nutrients to create more sustainable agricultural production systems. Trace elements (TEs) can be transferred to soils during application of digestate as fertilizer, being subjected to environmental influences. To evaluate TEs bioavailability and uptake by plants (which can be transferred to the food chain), TEs leaching processes (which can prevent loss of soils nutrients and run off in ground waters), and TEs effects on soil organisms (which can affect soil fertility and productivity), it is relevant to assess the fate and availability of TEs after land application of digestate. This book chapter provides an overview of different type of biogas plants and digestate post-treatment processes. Possible physicochemical interactions between digestate and soil components, which influence TEs speciation and availability for biological uptake, are also described. Finally, different TEs fractionation and speciation techniques are extensively discussed to give to the reader a good basis when investigating the fate of TEs in soils after digestate application.