The 4000 series is the general classification used to refer to the industry standard integrated circuits which implement a variety of logic functions using CMOS technology. They were created in the 1960s as a lower power and more versatile alternative to the 7400 series of TTL logic chips. Almost all IC manufacturers have fabricated this series in part or whole over the years.

Initially, the 4000 series was slower than the popular 7400 TTL chips, but had the advantage of much lower power consumption, the ability to operate over a much wider range of supply voltages, and simpler circuit design due to the vastly increased fanout. However their slower speed (initially only capable of about 1MHz operation, compared with TTL's 10MHz) meant that their applications were limited to static or slow speed designs. Later, new fabrication technology largely overcame the speed problems, while retaining backward compatibility with most circuit designs - a circuit could be made much faster by simply dropping in the newer chips. Eventually, the advantages of the 4000 series edged out the older TTL chips, but at the same time ever increasing LSI techniques edged out the modular chip approach to design. The 4000 series is still widely available, but perhaps less important than it was two decades ago.

The 4000 series permits the use of "cookbook" design, where standard circuit elements can be created and shared, and connected to other circuits with few, if any, connection difficulties. This greatly speeds up the design of new hardware by reusing standard approaches to circuit design. In contrast, TTL circuits, while similarly modular, often reqired much more careful interfacing, since the limited fanout (and fan-in) meant that loading of each output had to be carefully considered. It is also much easier to prototype LSI designs using the 4000 series and get repeatable and transferrable results when moving to the more integrated design.

The series was extended in the late 1970s and 1980s to include new types which implemented new or more greatly integrated functions, or were better versions of existing chips in the 4000 series. Most of these newer chips were given 45xx and 45xxx designations, but are usually still regarded by engineers as part of the 4000 series.

Example common 4000 series chips

• 4000 - dual 3-input NOR gate + 1 NOT
• 4001 _ quad 2_input NOR gate
• 4002 - dual 4-input OR gate
• 4008 - 4 bit Full adder
• 4011 - quad 2-input NAND gate
• 4012 - dual 4-input NAND gate
• 4013 - dual D-type flip-flop
• 4015 - dual 4-bit shift register
• 4017 - decade counter with decoded outputs
• 4022 - 4-bit binary up/down counter
• 4023 - triple 3-input NAND gate
• 4025 - triple 3-input NOR gate
• 4026 - dacade counter with 7-segment display driver
• 4030 - quad 2-input XOR gate (obsoleted by 4070)
• 4038 - dual monostable timer
• 4040 - 12-stage divider/counter
• 4044 - 7-segment display decoder/LCD driver
• 4049 - hex NOT gate (6 NOT gates) (unusual pin configuration, capable of directly driving 74-series TTL)
• 4050 - hex BUFFER (6 non-inverting buffers) (unusual pin configuration, capable of directly driving 74-series TTL)
• 4068 - 8-input NAND/AND gate
• 4069 _ hex NOT gate (6 NOT gates)
• 4070 - quad 2-input XOR gate
• 4071 - quad 2-input OR gate
• 4072 - dual 4-input OR gate
• 4073 - triple 3-input AND gate
• 4075 - triple 3-input OR gate
• 4077 - quad 2-input XNOR gate
• 4081 - quad 2-input AND gate
• 4082 - dual 4-input AND gate
• 4093 - quad 2-input NAND gate Schmitt trigger