Springer-Verlag began publishing books in higher mathematics in 1920, when the series <I>Grundlehren der mathematischen</I> <I>Wissenschaften</I>, initially conceived as a series of advanced textbooks, was founded by Richard Courant. A few years later, a new series <I>Ergebnisse der Mathematik und Ihrer</I> <I>Grenzgebiete</I>, survey reports of recent mathematical research, was added.<BR>Of over 400 books published in these series, many have become recognized classics and remain standard references for their subject. Springer is reissueing a selected few of these highly successful books in a new, inexpensive softcover edition to make them easily accessible to younger generations of students and researchers.