Physiological and biochemical traits hold great promise for demographic research as potential proxies (biomarkers) of various biotic and environmental variables that determine individual fitness and ultimately demographic rates. Integrating such biomarkers into demographic models can thus provide insights into drivers of population dynamics or increase predictive power of the models by refining estimation of vital rates. Biomarkers also represent promising means to characterise population structure and dynamics on much shorter time-scales compared to classical demographic approaches. Functional traits further emerge as direct targets of conservation efforts directed towards conserving functional diversity. Yet, biomarkers and functional traits remain underutilised in demography and population ecology, indicating that their benefits still await wider recognition. This chapter briefly reviews the most prominent physiological and biochemical traits (e.g. metabolic rates, hormones, oxidative stress markers, telomeres) that may be of interest in animal and plant demographic research, including the methods for collection, storage, and analysis, and the criteria to be met before the trait is validated as a biomarker. Hopefully, this effort will stimulate further integration of physiological and biochemical data into demographic framework.