E minor scale on octave mandola
The dark key of the tradition. Written E minor covers a family of tunes that in practice drift between minor and dorian, which is why the C in them comes and goes.
Hear the scale, played on the banjo voice
The notes
Every note above sits in first position on a GDAE-tuned octave mandola: nothing higher than fret 7, and each note has one home. Learn the scale as a shape and your fingers know where every note of every E minor tune lives before you have heard it.
The chords that go with it
This is the connection that makes session playing make sense. The backer's chords are built from the same 7 notes as the scale, so when the guitar holds Em, anything you play from the E minor scale fits. Melody players who seem to improvise freely are doing exactly this: decorating the tune with notes that never leave its own scale. Shapes for every chord here are on the octave mandola chord page.
Written minor keys in the tradition are a family rather than a fixed scale: the sixth note comes and goes, so many of these tunes lean dorian in practice. Play what the tune gives you rather than the textbook.
Tunes in E minor
142 of the 2701 tunes on this site are recorded in Em. A dozen to start on, in alphabetical order - every one has free GDAE tab, playback and the ABC source.
Questions about E minor
E, F#, G, A, B, C, D, E. On a GDAE-tuned octave mandola the whole scale sits in first position, between the open strings and fret 7.
Em, D, G carry most tunes in E minor, with C, Am as passing and turnaround chords. Two or three chords are enough: Irish accompaniment stays out of the tune's way.
In an Irish session the chord follows the tune, not the other way round. If the tune is in E minor, every note of the scale above fits over its chords, including Em and D and G. That is how melody players improvise variations without reading anything: they stay inside the tune's own scale.
This site's collection has 142 tunes recorded in Em out of 2701 in total, each with free GDAE tab. The corpus is O'Neill's 1903 and 1907 collections plus Kerr's Merry Melodies, so the balance reflects the tradition as it was written down.