pg SQL question

There's probably an obvious answer for this, but I couldn't see it in the
docs. What's the simplest way to concatenate multiple same-column values
in SQL?

For example, suppose I have table foo (key integer, id integer, entry
varchar) with data

key id entry
1 1 "Four score and seven years ago our fathers "
1 2 "brought forth on this continent, a new nation, "
1 3 "conceived in Liberty, and dedicated to the "
1 4 "proposition that all men are created equal."

and I want to produce the following result:

"Four score and seven years ago our fathers brought forth on this continent,
a new nation, conceived in Liberty, and dedicated to the proposition that
all men are created equal."

I know this could be done writing a plpgsql function, but it seems so basic,
I thought there might be something I'm overlooking.

TIA.

Ed