The regulations concerning the placement of biostimulants on the market are still widely varying across countries and regions, even though both efficacy claims and composition declarations are primarily addressed. The definition of pre-market approval systems specifying the data required for authorization is a key factor to protect the market of biostimulants. A combination of laboratory trials and dedicated ad hoc field studies are recommended to better address the definition of both mode(s) of action and effect(s) for plant biostimulants. Traditionally, in vitro assays (e.g. hormone-like activity tests) have been used to support the investigation of potential biostimulant activity. In recent years, the recent advances in analytics, technology and big data management have raised up the potential of -omic sciences in screening, evaluation and understanding regarding the mode of action for biostimulants. Provided the complementarity of different -omics, metabolomics and phenotyping are those adhering to actual phenotype, and are attracting a growing interest.