A word about terminology: "printed music" is here used to refer to contemporary printed editions of music scores.

"Sheet music" usually refers to historic printed music (generally popular, but sometimes "classical") from the 19th and early 20th centuries. For more information about historic sheet music, see Illinois' own historic sheet music collections.

There are different types of editions for printed music and which you choose depends upon what you need it for. You might need more than one edition of a work for comparison purposes.

• Critical edition: often referred to collected works or monuments, these editions include scholarly background information and commentary about the works and are carefully edited. Usually found in the M2s and M3s in the Reference section, these items don't circulate and are not meant to be performed from in most circumstances.
• Performing edition: these are the scores that you will find on the second floor of MPAL in our circulating collection. These vary greatly in quality based on publisher and editor, and your studio professor will likely have strong opinions about which ones you should use. Some include a lot of editorial marks (bowings, breath marks, fingerings, etc.) and may be unique to that editor (often a famous performer). Editions from publishers like Henle and Wiener Urtext are generally of good quality, while editions from publishers like International Music should be used cautiously. 
• Urtext: "A term used in studying and editing musical sources to signify the earliest version of the text of any composition, musical or otherwise, a version that is usually no longer extant; it is also used to signify a modern edition of earlier music which purports to present the original text, without editorial addition or emendation." (from Grove Music Online)

Full score

shows all instruments/voices in a work of music.

Miniature score (or study or pocket score)

Shows all instruments/voices in a work of music, but produced in a small size. Call numbers start with "MM" and are shelved separately from the other scores in our collection.

Vocal score (or piano-vocal score)

for operas or other choral/orchestral works; provides the vocal parts and presents the instrumental parts in a piano reduction or accompaniment.

Score and parts (or just parts)

For chamber music (2 or more players/singers) the printed music may be a score, showing all parts together, and/or include separate parts, one for each performer and their voice/instrument.

Just the parts and no score:

Or, a quartet with score and parts included:

Piano reduction or arrangement

Usually for concertos, presents the soloist's part and and presents the orchestral parts in a piano reduction or accompaniment.

Arrangement

when a work is originally written for one instrument or instruments and is arranged for another instrument or instruments.