Highland dress has been traditionally worn by the Scottish for centuries; however, the trend did not originally belong to the Scots. The Scots are historically the Lowlanders of the area and viewed the Highlanders as completely barbaric. As time passed and this rivalry ended, the concept of 'clan tartans' came to be and the Lowlander Scots adopted the Highland dress as their own and now wear it proudly as a sign of their family heritage. This outfit in particular is tradtionally worn by men.

Traditional Highland dress is typically brought out for parade, the Highland Games, dances, festivals, bagpipe playing, and formal events such as weddings.They are also worn by people in the service.

The Kilt: Originating from a long length of tartan cloth which was wrapped around a man's body, belted at the waist and pinned at the shoulder, the kilt has developed into a more complex garment these days. The kilt was chosen because it is warm, it does not restrict movement, and when made out of the traditionally tightly woven wool it is almost completely waterproof. The tartan only ever goes over one should in order to keep a man's sword arm free at all times. Much of a man's stature is derived from his kilt, which is why the kilts are traditionally worn for all formal and cultural occasions. In some cases, the kilt can be replaced with a trew, a modern trouser version of the kilt.

The Sporran: This purse-like accessorie is both fashionable and functional. One of the oldest and untouched pieces of the Highlander dress, the sporran is effectively the pocket of the outfit. The sporran must be worn at the front of the kilt and should hang between two or three inches below the belt of the kilt. Sporrans can be made of leather or fur or a combination of the two. The more ornamental sporrans have metallic features and are typically worn for more formal occasions. 

Ghillies: The leather shoes of Highlander dress are thick-soled, completely tongueless, and high laced over long socks or hose. The shoes were originally made without tongues so that the wearer's feet would dry off quickly if they were to get wet, and the laces were made to tie so far up the leg so that the shoes could not be pulled off if someone were trudging through thick mud. These days, most men where ghillie brogues which look much like dress shoes without the tongue and with extra lacing. Ghillies are more reserved for women's styles and for dancing.

Sgian Dubh: The name of this knife is derived from the Gaelic which means 'black wood', representative of the black bogwood commonly used for the handle of the knife. This single edged knife is traditionally tucked away in the man's stocking. The hilt of the knife remains visible out of the top the of sock, which is why the hilt is very ornate. Traditionally it is a utility knife for the owner, primarily employed for the preparation of fruit, the cutting of materials, or protection from wildlife. Nowadays, this knife is merely ceremonial piece of the Highlander dress and is considered more as a piece of art than as a tool.

Sources:

http://www.tartansauthority.com/highland-dress/

http://en.wikipedia.org/wiki/Highland_dress

http://www.tartansauthority.com/highland-dress/

http://www.piobmhor-of-scotland.co.uk/hdhistory.htm

http://www.scottish-history.com/kilt.shtml

http://www.westcoastkilts.com/kilt-history/kilt-history/