Most briefcases are derived from a limp satchel used in the fourteenth century for carrying money and valuables. It was called a "budget" derived from the Latin word "bulga" or Irish word "bolg" both meaning leather bag, and that’s where we also get the financial term.

Godillot of Paris first used a hinged iron frame on a carpetbag in 1826. Then followed the Gladstone bag and the Rosebery, an oval-top bag. Eventually these became the modern metal frame briefcase. Briefcases were, of course, named for the purpose of carrying attorney’s briefs.

Types of Briefcases:

Portfolio -- A case without handles to be carried in hand or under the arm.  The name comes from the Italian "portare" meaning "to carry" and "foglio" a "sheet".

Folio case – A portfolio with a retractable handle

Attaches – A diplomatic officer attached to an embassy or consulate officially 
assigned to serve in a particular capacity: a cultural attaché; a military attaché. 

The type of briefcase carried by such a person. A box style case, of leather stretched over a frame that opens into two hinged compartments.

Developed from the 19^th century portmanteau (from Old French porter, meaning to carry) a suitcase with split hide stuck to a stiff millboard foundation. The reduced size version became the attaché.

Trends:

We’ve seen a casual trend in recent history, which has carried through to the briefcase. Soft leather, often with shoulder straps has replaced traditional hard rectangular cases. The soft leather cases are more conductive to packing and expanding (you can cram more into them) plus they project a friendlier image. Another factor is the development of a laptop case for your traveling computer.

So look for new waves of knapsacks, backpacks, and messenger bags.