The rules of Victorian etiquette were extremely complicated and for good reason: many of them were once used only at court or amongst the nobility of England. As the middle class steadily gained footing within society due to the Industrial Revolution and the rise of small merchants, the rules became more widely adopted, and therefore more complicated. Here is just a small sampling of the complex social rules that were prevalent during the 1800s.
New friends had to be introduced properly and this was especially true for opposite-sex interactions. A young man approaching a pretty girl on the street would never do in polite society. Rather, a suitable mutual friend or family member of higher social status had to make the introduction, in effect sanctioning the socialization of the two individuals at all.
Letters of introduction were especially important during this time as a voucher for the character of the “lower” person, especially in the physical absence of the introducer, such as when traveling or upon a job interview. These letters were considered social gold and were not at all taken lightly.