Most RDBMSs support both syntaxes:
SELECT ...
FROM table1 t1 JOIN table2 t2
ON t1.jfield = t2.jfield
as well as
SELECT ...
FROM table1 t1, table2 t2
WHERE t1.jfield = t2.jfield
Personally, I prefer the latter version because of less verbosity but does it presents any difference in performance and query execution? I have seen people on this forum making remarks that the 2nd style is obsolete and does not perform as well.