Here's an example applying a recursive CTE, using an algorithm from
Molinaro's _SQL Cookbook_ (note: best viewed with fixed font):

WITH
    PARTICIPANT_NAME
    (
    PRTCP_NM_ID,
    PRTCP_ID,
    FIRST_NM
    )
AS
    (VALUES (1,1,'JEFF'),
    (2,1,'JEFFREY'),
    (3,2,'EDDIE'),
    (4,2,'EDWARD'),
    (5,2,'TED'),
    (6,3,'ELIZABETH')
    ),
    PRTCP_NM
    (
    PRTCP_ID,
    CNT,
    LIST,
    PRTCP_NM_ID,
    LEN
    )
AS
    (
    SELECT
        PN1.PRTCP_ID,
        COUNT(*) OVER (PARTITION BY PN1.PRTCP_ID),
        CAST(PN1.FIRST_NM AS VARCHAR(4000)),
        PN1.PRTCP_NM_ID,
        1
    FROM
        PARTICIPANT_NAME PN1
    UNION ALL
    SELECT
        PRTCP_NM.PRTCP_ID,
        PRTCP_NM.CNT,
        PRTCP_NM.LIST||', '||PN2.FIRST_NM,
        PN2.PRTCP_NM_ID,
        PRTCP_NM.LEN + 1
    FROM
        PARTICIPANT_NAME PN2,
        PRTCP_NM
    WHERE
        PN2.PRTCP_ID = PRTCP_NM.PRTCP_ID
    AND
        PN2.PRTCP_NM_ID > PRTCP_NM.PRTCP_NM_ID
    )
SELECT
    LIST
FROM
    PRTCP_NM
WHERE
    LEN = CNT

and here's a really cool example--from this forum, BTW--of using the
XMLAGG function:

CREATE TABLE EMPLOYEE(NAME VARCHAR(15), DEPT VARCHAR(15));

NAME    DEPT
-----   ------
MISO    SOLUTIONS
JOHN    DEVELOPMENT
SERGE   SOLUTIONS
LEE     L3
MARK    ID
JACK    L3
LILY    QUALITY
BERNI   SOLUTIONS

SELECT DEPT,
       SUBSTR(NAMES, 1, LENGTH(NAMES) -1)
  FROM (SELECT
          DEPT,
          REPLACE
           (REPLACE
            (XMLSERIALIZE
             (CONTENT XMLAGG(XMLELEMENT(NAME A, NAME)
                             ORDER BY NAME)
              AS VARCHAR(60)), '<A>', ''), '</A>', ',') AS NAMES
         FROM EMPLOYEE GROUP BY DEPT) AS X;

DEPT            NAMES
-----           --------------------
SOLUTIONS       BERNI, MISO, SERGE
DEVELOPMENT     JOHN
L3              JACK, LEE
ID              MARK
QUALITY         LILY

HTH,

--Jeff