Some college applications allow applicants to attach an essay as a file. The Common Application and many online forms will automatically format your essay, so you have no say when it comes to spacing. If the school provides no guidelines, either single- or double-spaced is fine with a slight preference for double-spacing. Should your personal statement be single-spaced so that it fits on a page?
How to Double Space Your Paper
Fonts and Line Spacing | Guide to the ALM Thesis
It only takes a minute to sign up. Connect and share knowledge within a single location that is structured and easy to search. The answer provided in this question does not work with classicthesis: Double line spacing. Since Classicthesis is used a lot for PhD theses, and a lot of these are required to be double spaced, I'm probably not the only one who's had this problem.
Headings and Subheadings
Academia Stack Exchange is a question and answer site for academics and those enrolled in higher education. It only takes a minute to sign up. Connect and share knowledge within a single location that is structured and easy to search. It is standard practice to require dissertations to be double-spaced.
This article is a guide to constructing a decent parent file for a thesis or dissertation compiled in Latex. The specific details implemented here, and included in the example files, are those set out by the guidelines for submission to the University of Nottingham, but can be easily amended to suit any sensible requirements. Considerable attention has been paid to presenting the final document as a PDF file, which keeps the file size manageable compared to postscript and allows groovy add-ons such as hyperlinks and back-referencing. However, several hacks are required to attain good functionality from your PDF file and these can give the latex code a mysterious and messy appearance in places. While I highly recommend the inclusion of the PDF-related commands, they are not strictly necessary and can be ignored - especially if you are new to Latex.