Not all cases appropriate for MDL are appropriate for class certification. Class certification requires common questions of law or fact, as well as a number of other criteria. With class certification, the preceding cases can, but need not be, in different federal district courts. In cases where MDL and/or class certification are available, the particular method selected is a strategic consideration.
Any real similarities or comparisons between the two methods ends there. There is a Judicial Panel on MDL made up of seven judges from different federal districts, appointed by the Chief Justice of the Supreme Court. During cases involving common questions of fact, any party in any of those cases can file a motion to transfer the actions under the MDL statute (28 U.S.C. 1407). The Judicial Panel can transfer cases on its own, but usually a party has to file a motion. The Judicial Panel decides whether to grant or deny motions to transfer before MDL, and whether to grant or deny motions to remand when MDL is complete. Here is a handy checklist for attorneys filing a new MDL motion.
Once a party files a motion to transfer any number of cases (two or more), the Judicial Panel sets the motion for hearing, notifying all parties in all districts that would be affected by the transfer. Filing a motion to transfer is an exercise in transcription, because one must include all parties in all cases where transfer is sought. If the motion is granted, copies of the order transferring the case are sent to each court from which a case is transferred. If the motion is denied, the order is filed only in districts where there is a pending motion to transfer.
If the motion is granted, MDL is only operative in pretrial proceedings. Pretrial proceedings in MDL cases are not conducted before the Judicial Panel, but are instead conducted in the court specified in the motion to transfer and its resultant order. When the cases are ready for trial, they are remanded to the district court from which they were transferred. If the Judicial Panel sees fit, it has discretion to separate claims, counterclaims and cross-claims before the pretrial proceedings are complete.