McLaren was fined a record US$100 million and lost the constructors' championship for possessing leaked Ferrari documents. While McLaren shoots for its first title in a decade, Italian police continue their investigation.
Alonso returns to Renault, where he made his name by becoming the youngest champion with back-to-back titles in 2005-06.
The French team has been playing catch-up ever since and offers slight expectations on his return.
Alonso is joined by a rookie teammate for the second straight year in Nelson Piquet Jr. -- son of 1987 champion Nelson Piquet. But it's the No. 1 status accorded to the 26-year-old Alonso that could see Renault surprise.
F1 boss Bernie Ecclestone hopes that's the case.
"I just hope that Fernando's car is as fast as Lewis' so we can see some real competition," Ecclestone said.
Renault should duel with BMW Sauber, Williams and Red Bull for the occasional podium place.
BMW Sauber was meant to contend by now, but winter testing suggests the German team is still off the pace.
Williams, led by Nico Rosberg -- son of 1982 champion Keke Rosberg -- could snatch third from BMW Sauber if it continues the good form it showed over the winter with its Toyota engines.
Rosberg, driving with Japanese rookie Kazuki Nakajima, is staying grounded after rejecting McLaren's vacant seat to stay at Williams, which hasn't won the title since 1997.
"We're aiming for fourth in the constructors' championship. Maybe some podiums with a little luck, but for that we'll need a lot of things to fall into place," the 22-year-old German said.
Honda recruited Ferrari technical director Ross Brawn after a poor campaign that saw it drop to eighth. Driver Jenson Button expects improvements after winning all six points -- only two better than Super Aguri.
Three-time Champ Car champion Sebastien Bourdais makes the jump to F1 with Toro Rosso alongside 20-year-old German driver Sebastien Vettel.