This seminar will focus on the role of marine emissions, both particles and those initially formed in the gas phase and converted to particles, on cloud formation.  Because the cloud-forming properties of aerosols depend on composition and size, consideration of differences in organic aerosol source provides insight on how marine biogeochemistry influences clouds.  Measurements of aerosol chemistry, cloud condensation nuclei, and ice nucleating particles will be presented. Findings from recent field measurements and laboratory experiments will be discussed in the context of open questions and current controversies.