&gt; What are the differences between postdocs, research assistants, research scientists and visiting scientists?<p>These are some working definitions, based on my experiences in astronomy:<p><i>Postdocs</i>: researchers with a a PhD who generally have fixed-term contracts. Generally these positions are full-time research, though some may include teaching components.<p><i>Research assistants</i>: researchers, typically without PhDs, working in a group&#x2F;lab. This is frequently a synonym for undergraduate or graduate students, or interns. It can also mean people with technical skills who are working in a group&#x2F;lab but not working towards a degree.<p><i>Research scientists</i>: Non-tenure track reseachers, often with PhDs. Their positions may be fixed-term or indefinite.<p><i>Visiting scientists</i>: Researchers whose primary affiliation is with another institute. They may be fixed-term visitors (e.g., faculty on sabbatical at another University) or frequent but non-constant visitors of an institution. Their salary is often paid by their primary institute, unless the host institute has provided funding.