Defence priming is defined as the enhanced sensitivity and responsiveness to stress that results from a prior experience and leads to increased resistance and/or stress tolerance. For plants, priming agents may be microorganisms or chemicals. This chapter reviews defense priming against plant pathogens when the priming agent is associated with seeds, concentrating on microbial endophytes and volatile organic compounds, and, where known, the mechanisms involved in defence responses. Whether these responses can be vertically transmitted between plant generations is also briefly discussed. Answers to nine research questions posed will contribute to turning the promise for seed defence priming into practice.