This text, based on course notes for the Berkeley course Math 245, "General Theory of Algebraic Structures" taught over the years, has now appeared in Springer's Universitext series, with ISBN 978-3-319-11477-4, eBook ISBN 978-3-319-11478-1, and DOI 10.1007/978-3-319-11478-1.
Here is the PDF file for the version I submitted to Springer, which has essentially the same content as that version.
If you have any corrections or comments, you can e-mail me: . I will maintain a file of errata and addenda online.
I maintain lists of answers to some questions submitted by students over the course of the semester. I've combined the lists from Spring 2008, Fall 2011, and Spring 2014 into this list, adjusting the references to the 2015 edition of the text. I will start a new list, when I teach the course in Fall 2015.