A Bachelor of Science (BS, BSc, SB, or ScB; from the Latin scientiae baccalaureus) is a bachelor's degree that is awarded for programs that generally last three to five years.

The first university to admit a student to the degree of Bachelor of Science was the University of London in 1860. In the United States, the Lawrence Scientific School first conferred the degree in 1851, followed by the University of Michigan in 1855. Nathaniel Shaler, who was Harvard's Dean of Sciences, wrote in a private letter that "the degree of Bachelor of Science came to be introduced into our system through the influence of Louis Agassiz, who had much to do in shaping the plans of this School."

Whether Bachelor of Science or Bachelor of Arts degrees are awarded in particular subjects varies between universities. For example, an economics student may graduate as a Bachelor of Arts in one university but as a Bachelor of Science in another, and occasionally, both options are offered. Some universities follow the Oxford and Cambridge tradition that even graduates in mathematics and the sciences become Bachelors of Arts, while other institutions offer only the Bachelor of Science degree, even in non-science fields.

At universities that offer both Bachelor of Arts and Bachelor of Science degrees in the same discipline, the Bachelor of Science degree is usually more focused on that particular discipline and is targeted toward students intending to pursue graduate school or a profession in that discipline.

In some institutions, there are historical and traditional reasons that govern the granting of BS or BA degrees regardless of the disciplines offered. Georgetown University's School of Foreign Service awards the Bachelor of Science in Foreign Service (BSFS) degrees to all of its undergraduates, although many students major in humanities-oriented fields such as international history or culture and politics. University of Pennsylvania's Wharton School awards the BS in Economics to all of its undergraduates, regardless if the candidates major in economics or not. The London School of Economics offers BSc degrees in practically all subject areas, even those normally associated with the arts and humanities. Northwestern University's School of Communication grants the Bachelor of Science in Journalism degrees in all of its programs of study, including theater, dance, and radio/television/film. Meanwhile, the Oxbridge universities almost exclusively award the BA as a first degree.

The decision to grant a BS or BA degree at some institutions also depends on the constituent colleges, even when the candidate pursues the same or similar subjects. For instance, Cornell University offers a BS degree in computer science from its College of Engineering and a BA degree in computer science from its College of Arts and Sciences. Likewise, for candidates majoring in computer science, Columbia University offers BS degrees for those enrolled in the School of Engineering and Applied Science but awards BA degrees for graduates of Columbia College. At Harvard University, the same undergraduate degree in computer science can be an A.B. if taken at Harvard College or Harvard John A. Paulson School of Engineering and Applied Sciences, and an A.L.B. at Harvard Extension School.

In Argentina most university degrees are given as a license in a discipline. They are specific to a field and awarded to students upon completion of a course of study which lasts at least four and usually five years. In most cases, at the end of a course and as a mandatory condition for its completion (and ultimately, to obtain a degree), students are compelled to produce an original research project related to their field. This project is usually referred to as a thesis (although the term actually corresponds to post-graduate studies).

In Australia, the BSc is generally a three to four-year degree. An honours year or a master's by research degree is required to progress on to the stage of Doctor of Philosophy (PhD).