Seed biology is important for emergence in the field and for future weed infestations. This chapter focuses on seed biology, germination, dormancy and efforts in predicting weed emergence from seeds from a European perspective. It presents a brief overview of population dynamics in time and space, the factors influencing the dynamics and how population dynamics can be modelled. Emergence from the seed-bank starts with germination, pre-emergence growth and finally emergence. In addition to seeds, vegetatively propagated material is briefly mentioned. Dormancy influences under what conditions that germination can occur and regulates timing of germination. Population dynamics are important for understanding the whole system and are often based on the life-cycle of weeds: seed-bank, seedlings, adult plants, seed production and dispersal. Challenges in modelling emergence and population dynamics are large, due to differences between and within populations of species, variability in species response and there being many weed species in the same field with contrasting characteristics.