References. It is assumed that you have references if you have previous employment history. It is not at all necessary to include “references available upon request”, adding this is actually a potential deterrent. Potential employers will ask you for your references later on in the interview process if they see fit. Of course, if references are asked for within the application process, provide them - just not on your resume.
In many cases, your resume is the first document a hiring manager will look at when reviewing your application, and therefore is a true “first impression.” Accordingly, it’s important to put time and effort into developing and maintaining an updated, accurate resume.