Resistive touchscreens are composed of two flexible sheets coated with a resistive material and separated by an air gap or microdots. When contact is made to the surface of the touchscreen, the two sheets are pressed together, registering the precise location of the touch. Because the touchscreen senses input from contact with nearly any object (finger, stylus/pen, palm) resistive touchscreens are a type of "passive" technology.

For example, during operation of a four-wire touchscreen, a uniform, unidirectional voltage gradient is applied to the first sheet. When the two sheets are pressed together, the second sheet measures the voltage as distance along the first sheet, providing the X coordinate. When this contact coordinate has been acquired, the uniform voltage gradient is applied to the second sheet to ascertain the Y coordinate. This operation occurs instantaneously, registering the exact touch location as contact is made.

Resistive touchscreens typically have high resolution (4096 x 4096 DPI or higher), providing accurate touch control. Because the touchscreen responds to pressure on its surface, contact can be made with a finger or any other pointing device.

Resistive touchscreen technology works well with fingertip input.
Costs are relatively low when compared with active touchscreen technologies.
Resistive touchscreen technology can also support multi-touch input.

Due to the nature of passive touchscreen design, when "inking" (taking handwritten notes with a stylus) multiple touches can lead to "vectoring", which can make note-taking difficult or impossible.
To avoid this problem, alternative touchscreen technologies are available, such as active touchscreen in which only the stylus creates input and touches from the hand are rejected.

Surface acoustic wave (SAW) technology uses ultrasonic waves that pass over the touchscreen panel. When the panel is touched, a portion of the wave is absorbed. This change in the ultrasonic waves registers the position of the touch event and sends this information to the controller for processing. Surface wave touchscreen panels can be damaged by outside elements. Contaminants on the surface can also interfere with the functionality of the touchscreen.

A capacitive touchscreen panel is a sensor typically made of glass coated with a transparent conductor such as indium tin oxide (ITO). This type of sensor is basically a capacitor in which the plates are the overlapping areas between the horizontal and vertical axes in a grid pattern. Since the human body also conducts electricity, a touch on the surface of the sensor will affect the electric field and create a measurable change in the capacitance of the device. These sensors work on proximity, and do not have to be directly touched to be triggered. It is a durable technology that is used in a wide range of applications including point-of-sale systems, industrial controls, and public information kiosks. It has a higher clarity than Resistive technology, but it only responds to finger contact and will not work with a gloved hand or pen stylus unless the stylus is conductive. Capacitive touchscreens can also support Multitouch. Examples include Apple Inc.'s iPhone and iPod Touch, HTC's G1 & HTC Magic, Palm Inc.'s Palm Pre and Palm Eos and more recently the LG KM900 Arena, Microsoft's Zune HD, Sony Walkman X series and Sony Ericsson's Aino.

Projected Capacitive Touch (PCT) technology is a type of capacitive technology which involves the relationship between an XY array of sensing wires embedded within two layers of non-metallic material, and a third object. In touchscreen applications the third object can be a human finger. Projected capacitance creates an electrostatic field above the sensing surface to determine inputs. This format requires the use of patterned ITO and requires no calibration. Capacitance forms between the user’s fingers and projected capacitance from the sensing wires. A touch is made, precisely measured, then passed on to the controller system which is connected to a computer running a software application. This will then calculate how the user’s touch relates to the computer software. PCT screens enjoy the benefits of responding accurately to both fingers and styli.

Visual Planet’s ViP Interactive Foil is an example of a product that uses PCT technology. This technology allows a gloved hand to make the touch, resulting in PCT technology now being common in external "through window" touch applications (i.e. those where no direct physical contact with the touchscreen is made).

Conventional optical-touch systems use an array of infrared (IR) light-emitting diodes (LEDs) on two adjacent bezel edges of a display, with photosensors placed on the two opposite bezel edges to analyze the system and determine a touch event. The LED and photosensor pairs create a grid of light beams across the display. An object (such as a finger or pen) that touches the screen interrupts the light beams, causing a measured decrease in light at the corresponding photosensors. The measured photosensor outputs can be used to locate a touch-point coordinate.

Widespread adoption of infrared touchscreens has been hampered by two factors: the relatively high cost of the technology compared to competing touch technologies and the issue of performance in bright ambient light. This latter problem is a result of background light increasing the noise floor at the optical sensor, sometimes to such a degree that the touchscreen’s LED light cannot be detected at all, causing a temporary failure of the touch screen. This is most pronounced in direct sunlight conditions where the sun has a very high energy distribution in the infrared region.

However, certain features of infrared touch remain desirable and represent attributes of the ideal touchscreen, including the option to eliminate the glass or plastic overlay that most other touch technologies require in front of the display. In many cases, this overlay is coated with an electrically conducting transparent material such as ITO, which reduces the optical quality of the display. This advantage of optical touchscreens is extremely important for many device and display vendors since devices are often sold on the perceived quality of the user display experience.

Another feature of infrared touch which has been long desired is the digital nature of the sensor output when compared to many other touch systems that rely on analog-signal processing to determine a touch position. These competing analog systems normally require continual re-calibration, have complex signal-processing demands (which adds cost and power consumption), demonstrate reduced accuracy and precision compared to a digital system, and have longer-term system-failure modes due to the operating environment.

Finally, infrared touch is not capable of multi-touch as a result of the mode of operation being one in which lines of light are disrupted. Thus for two points, two beams would be disrupted on both the horizontal and vertical axes each, allowing for a total of four potential point locations. This ambiguity makes infrared unsuitable for multi-touch applications.

Neonode has taken conventional infrared touch technology, using LEDs and photodiodes, and essentially miniaturized it and reduced the cost for use in handheld devices. In addition to using the technology in its own N2 cell phone, Neonode is also marketing it to other device makers.

A relatively-modern development in touchscreen technology, two or more image sensors are placed around the edges (mostly the corners) of the screen. Infrared backlights are placed in the camera's field of view on the other sides of the screen. A touch shows up as a shadow and each pair of cameras can then be triangulated to locate the touch or even measure the size of the touching object. This technology is growing in popularity, due to its scalability, versatility, and affordability, especially for larger units.

Introduced in 2002 by 3M, this system uses sensors to detect the mechanical energy in the glass that occurs due to a touch. Complex algorithms then interpret this information and provide the actual location of the touch. The technology claims to be unaffected by dust and other outside elements, including scratches. Since there is no need for additional elements on screen, it also claims to provide excellent optical clarity. Also, since mechanical vibrations are used to detect a touch event, any object can be used to generate these events, including fingers and stylus. A downside is that after the initial touch the system cannot detect a motionless finger.

This system, developed by Tyco International's Elo division, uses more than two piezoelectric transducers located at some positions of the screen to turn the mechanical energy of a touch (vibration) into an electronic signal. The screen hardware then uses an algorithm to determine the location of the touch based on the transducer signals. This process is similar to triangulation used in GPS. The touchscreen itself is made of ordinary glass, giving it good durability and optical clarity. It is usually able to function with scratches and dust on the screen with good accuracy. The technology is also well suited to displays that are physically larger. As with the Dispersive Signal Technology system, after the initial touch, a motionless finger cannot be detected.

Multi-touch (or multitouch) denotes a set of interaction techniques which allow computer users to control graphical applications with several fingers.

Multi-touch consists of a touch screen (screen, table, wall, etc.) or touchpad, as well as software that recognizes multiple simultaneous touch points, as opposed to the standard touchscreen (e.g. computer touchpad, ATM), which recognizes only one touch point. This effect is achieved through a variety of means, including but not limited to: heat, finger pressure, high capture rate cameras, infrared light, optic capture, tuned electromagnetic induction, ultrasonic receivers, transducer microphones, laser rangefinders, and shadow capture.

Many applications for multi-touch interfaces exist and are being proposed. Multi-touch is often associated with Apple Inc's iPhone and iPod Touch but is also used in many other products such as Apple's MacBook and MacBook Pro notebook line, Microsoft Surface, Asus Eee PC, Meizu M8 , HTC Hero and the upcoming Zune HD. Other products such as the Blackberry Storm and the HTC Dream are multi-touch capable, but have no official software to take advantage of the function.

Mainstream exposure to multi-touch technology occurred in the year 2007, when Apple unveiled the iPhone and Microsoft debuted surface computing. The iPhone in particular has spawned a wave of interest in multi-touch computing, since it permits greatly increased user interaction on a small scale. More robust and customizable multi-touch and gesture-based solutions are beginning to become available, among them TrueTouch, created by Cypress Semiconductor. The following is a compilation of notable uses of multi-touch technology in recent years.

In 2005, Apple acquired Fingerworks. In 2007 they introduced the iPhone, marking the first time multi-touch technology was used on a phone. The iPhone includes such components as a web browser, music player, video player, and a cell phone without the use of a hard keypad or stylus.

Following the release of the iPhone, Apple also expanded its use of multi-touch computing with the new iPod Touch, as well as the new MacBook Air. As of 2008, Multi-touch can be found on the MacBook and MacBook Pro line in the form of a trackpad.

The latest revisions of Apple's Unibody MacBook and MacBook Pro features a full glass multi-touch trackpad (whilst the MacBook Air features a standard multi-touch trackpad). These enable various gestures such as scrolling, "swiping" between pages or pictures as well as rotating pictures, and launching Expose. Apple has patented its “Multi-Touch” technology.

In 2001 Steve Bathiche and Andy Wilson of Microsoft began work on an idea for an interactive table that mixes both physical and virtual worlds. Research and Development expanded rapidly in 2004, once the idea caught the attention of Microsoft Chairman Bill Gates. In 2007 Microsoft introduced Microsoft Surface, a functional multi-touch table-top computer based on a standard PC platform including an Intel Core 2 Duo processor, Windows Vista, and 2 GB of RAM.

Essentially, Microsoft Surface is a computer embedded in a table with a large, flat, touch-responsive display on the top. The table uses small cameras (as opposed to finger pressure or heat) that enable it to react to the touch of any object. The unit has eight different modes that allow users to perform an array of activities,ranging from organizing pictures and videos to ordering food at a restaurant. Multiple users have the ability to work on the table at one time. The preliminary launch was on April 17, 2008, when Surface became available for customer use in AT&T stores. The price for one unit is said to range somewhere between $5,000 and $10,000.

Windows 7 will support Multi-touch. The operating system is known to have a multi-touch mapping application, photo viewing program, and incorporation in Internet Explorer 8. In January 2009, Microsoft joined with other investors who invested twenty-four million dollars in N-Trig Ltd., which plans to make computer hardware that takes advantage of Windows 7's multi-touch support.

HP Touchsmart is an All-In-One PC introduced by computer giant Hewlett-Packard and was first released in 2007. It is an example of the PC-In-A-Box terminology quite similar to the iMac G3 except that it utilizes more modern concepts such as better performing hardware, Windows Vista OS and of course, its 19"+ flat panel multi-touch display. It is the first mass marketed 'touch screen' PC made commercially available.