Prime time is that portion of the evening when the American audience levels for television viewing are at their highest. In the Eastern and Pacific time zones, prime time is 7:00 - 11:00 p.m., in the Central and Mountain time zones prime time is 6:00 - 10:00 p.m.. The 9:00 p.m. hour (Eastern and Pacific) and the 8:00 p.m. hour (Central and Mountain) have the highest HUT (homes using television) level.

The commercial broadcast networks have always attracted the largest portion of the prime time viewing audience. Through the 1960s, it was not unusual for the three networks to attract 85%-90% of the available prime time audience. The remaining 10%-15% of the audience would be watching programming available on independent television stations or on public television stations.

Broadcast networks pay their affiliated stations in each local market to air the network offerings (this is called network compensation). In return, the networks retain the bulk of the commercial time for sale to national advertisers. This arrangement works well for both parties--the networks attract audiences in each local market for their programming, which enables them to sell commercial time during such programs to advertisers wanting to reach a national audience. The local affiliated television stations receive high quality programming, payment from the network, and the opportunity to sell the remaining commercial time (usually about one minute each hour) to local advertisers.

In the mid-1990s, the average 30-second prime time network television advertising spot cost about $100,000. These same spots on a top-rated series average about $325,000, and such spots on low-rated network prime time programs average, about $50,000. Top-rated prime time spots in local television markets can cost as much as $20,000.

Because of network dominance in prime time, independent television stations (those not affiliated with a major broadcast network) have found it difficult to compete directly with network-affiliated television stations during these most desirable hours. In an attempt to allow independents to compete somewhat more fairly, during at least a portion of prime time, the Federal Communications Commission (FCC) enacted the Prime Time Access Rule (PTAR). The rule limits the amount of time a local affiliate can broadcast programming provided by the network. The most recent version of PTAR became effective in September 1975. It basically limited network-affiliated television stations in the 50 largest markets to no more than three hours of network (or off-network syndicated) programming during the four hours of prime time. The three hour limit may be exceeded if the additional programming is public affairs programming, children's programming, or documentary programming, or if the additional programming is a network newscast that is adjacent to a full hour of local newscasts. Other exceptions to the three hour limit include runover of live sporting events, and feature films on Saturday evenings.

The growth of cable television in the 1980s resulted in a plethora of viewing options for the audience. Where audiences once had a choice of up to five, perhaps six options at any point in time, the new multi-channel environment provided viewers with more than 50 programming choices at once. In addition, the advent of the video cassette recorder (VCR) also enabled viewers to rent pre-recorded tapes, or to time-shift (watch programs that were recorded at an earlier time). The result of all this increased competition is that the networks' share of the audience declined throughout the 1980s and 1990s. This was most evident in the prime time hours. By the 1990s the networks' share of the audience had dropped from their routine 80%-90% to 60%-65%. And as cable and VCR penetration levels (63% and 79%, respectively in 1995) continue to grow, the fate of network television in prime time may decline once again.

According to Shapiro (1992), while prime time programming has changed much during the first 45 years of television, three main trends continue: (1) the continued growth of the situation comedy; (2) the continued decline and ultimate death of the variety show; and (3) the consistent appeal of drama.

As new technologies, increased competition and decreased regulation of television systems have developed throughout the world in the late decades of the twentieth century, the notion of prime time has become more and more prevalent in systems outside the United States. Where television programming was once a special activity, often a limited number of hours roughly equivalent to American prime time, the move toward 24-hour programming has added new significance to the evening hours. Prime time is now a common marker in the days of citizens around the globe and this televisual "clock" has become part of everyday experience in almost every society.

-Mitchell E. Shapiro