The norms for ordering multiple authors vary between disciplines. Journals usually leave the choice of the ordering to be determined by the authors. The two main ordering criteria are the authors' last name (alphabetical order) and the importance of their contribution to the research (contribution order).
It is frequent to combine the alphabetical and the contribution criteria, so that the researcher who has contributed most occupies the first place in the list of co-authors and the rest of co-authors are ordered alphabetically. In many scientific disciplines, the last author in the list is the researcher who is responsible for the accuracy of the results; usually, this is the principal investigator of the research project or the head of the department.