An excellent introduction to the book of Psalms is that of Erich Zenger entitled "Das Buch der Psalmen" in Erich Zenger et al., Einleitung in das Alte Testament (5th ed., Studienbuecher Theologie 1/1; Stuttgart: Kohlhammer, 2004). One volume of a three volume commentary on the Psalms by Zenger and Frank-Lothar Hossfeld has appeared in English (Psalms 2: A Commentary on Psalms 51-100 [Hermeneia; Minneapolis: Augsburg Fortress, 2005]).
The introduction and notes on the Psalms by Adele Berlin and Marc Zvi Brettler in The Jewish Study Bible (Oxford: Oxford University Press, 2004) are also excellent.
The brief introduction I offer is not a mere rehash of the work of others. It will be of interest to seasoned scholars and beginners alike.
Go to: IntroPsalms.pdf