Selecting new windows takes more than just going with the looks that match the house they are about to be built in. Aside from acting as source of daylight and architectural accent, windows also give shape to the room, provide ventilation and emergency escape route. These are the most popular window styles.
Broad Division
Generally speaking, windows can be fixed or operable. Fixed windows re used solely as architectural feature in places where there is need for natural light and view but ventilation is not a concern. They often come in unusual geometric shapes like round-tops or relatively new type of seamless bent-glass windows that provide unobstructed corner view. However, operable windows are what most people consider for their homes. They can be sided sideways, vertically or hinged outwards or inwards on both vertical and horizontal panes.

Double Hung and Tilt-Turn Windows
This classic design has survived centuries and not without a reason. Apart from having excellent ventilation control, they have a very simple construction. Their upper outside sash can be lowered, while the lower inside sash can slide up. Some types even feature sashes that can be removed easily for cleaning. A sub-variant of this type with only one sliding sash is called single-hung. Tilt-turn windows are popular in Europe. They tilt inside at the top but also have a feature that allows them to swing at 180 degrees for easier cleaning, which doubles as convenient emergency exit.
Casement Windows
These side-mounted windows are made in single or paired configuration and are operated by a crank that rotates the sash inward or outward. They can be fully opened for easy cleaning and maintenance, while their excellent ventilation properties come from their breeze catching effect, in which they act like sails on a boat.
Awning and Hopper Windows
It is easiest to describe them as horizontal casements. While awning windows are top hinged, so that they offer partial ventilation, unobstructed views and respectable security. Hopper windows are their inverted image. They hinge at the bottom and due to their very good ventilation properties are often used as a complement for a door or another window.

Horizontal Sliding Windows
They feature a single or multiple panels that are fixed and one or more panels that slide in horizontal tracks. The drawback of this design is that in the best case only half of the window can be opened at a time, providing only partial ventilation. However, an advantage of sliders is that no space is required for a sash to swing in or out, making them ideal for small spaces.
Bay Windows
This three-window set is easily recognized from the outside as it protrudes from the house wall, and forms an interior bay. In addition to great light gathering characteristics, bay window offers much wider view angle than any other type, save the seamless corner windows. A central window is flanked by two side ones that make 30 or 45 degree angle with the house wall.
In order to fulfil their different needs, windows come in many sizes, types and functions. When choosing windows for your home, consider architectural aspect, the window purpose and budget.