You could do this with a User Defined Function (UDF). Put the UDF into a
code module and then reference it in a cell just like you would any other
Excel worksheet function. Using your example, where test value is in column
A and values to be concatenated are in column B, this should work as a UDF:

Private Function BuildLongList(TestValue As Variant)
Dim LC As Long

Application.Volatile
Do While LC <= Range("A" & Rows.Count).End(xlUp).Row
If Range("A1").Offset(LC, 0) = TestValue Then
BuildLongList = BuildLongList & Range("B1").Offset(LC, 0) & ", "
End If
LC = LC + 1
Loop
If Right(BuildLongList, 2) = ", " Then
BuildLongList = Left(BuildLongList, Len(BuildLongList) - 2)
End If
End Function

Then in the cell(s) where you want the results to show up you would put
formula similar to these, first example for any cell other than A1 or B1 in
row 1, and second for any cell other than A9 or B9 in row 9:
=BuildLongList(A1)
=BuildLongList(A9)


" wrote:

Lets say I have
A1 has value "Y", Cell B1 having value : ABC
A1 has value "Y", Cell B2 having value : DEF
A1 has value "N",Cell B3 having value : GHI
...
...
...
An has value "Y", Cell Bn having value : LKJ

I wish to concatenate all these text into one single cell, based on a
condition

for ex:
For all records wherein I have value of Ai = "Y", I wish to have a
comma separated list of all values in Cell Bi

Is there a formulae which i can use for concatenating this range of
values

Would appreciate all help from your side

thanks
Subda