Let's suppose list A in colummn A, list B in column B and list C in
column C. Define ListA as referring to :
=OFFSET(Sheet2!$A$1,,,COUNTA(Sheet2!$A:$A))
same thing for ListB and ListC
Select column B and with data validation list, enter the formula :
=IF(A1="a",ListA,IF(A1="b",ListB,IF(A1="c",ListC," ")))
For better understanding, here is the sample file :
http://www.filedropper.com/081120
HTH
Daniel

I have 3 lists defined in worksheet 2, lists A, B, C. In worksheet 1, the
cells in column A will equal either A, B, or C. I want the dropdown list in
column 2 to be conditional of the value in column 1.

column a column b
A List A
C List C
A List A
B List B

etc...

I'm having a lot of trouble figuring this one out. Any ideas or help?