Dress
The dress in Peru varies greatly as many young people and the urban populations tend to wear western-styled clothing, while many of the Quechua prefer to wear more traditional clothes. The style of the clothing many Quechua wear today is not wholly authentic as their "traditional" dress tends to be a combination of pre-Columbian and Spanish in style, design, and even fabric.
Today the traditional dress worn by many of the Quechua women in Peru is centered on a polleras, which is a skirt generally made from wool. These polleras have many variations and often times these differences are regional as many locals can tell where an individual is from based on her polleras. Women also tend to wear monteras, which are hats, and k'eperina, which are large sheets of cloth used to carry goods from the market, the farm, or even children. Both Quechua women and men also tend to wear ajotas, which are sandals made from recycled tires. Men who wear traditional Quechua clothes tend to wear a poncho, which is typically red. Again the designs on these vary and can indicate where an individual is from, but today few men wear this except on important special occasions.
As a visitor to Peru you should dress conservatively by covering your legs and shoulders at a minimum. However, wearing shorts or t-shirts will rarely cause offense and are more likely just going to get you stares from curious locals. If you want to fit in with the local youth in cities like Lima try on a soccer jersey (football kit) and track pants. Or fit in with the older population by wearing dark woven coats and pants. In business settings stick with western-styled suits and other professional dress.