A picosecond (abbreviated as ps) is a unit of time in the International System of Units (SI) equal to 10⁻¹² or 1⁄1 000 000 000 000 (one trillionth) of a second. That is one trillionth, or one millionth of one millionth of a second, or 0.000 000 000 001 seconds. A picosecond is to one second as one second is to approximately 31,689 years. Multiple technical approaches achieve imaging within single-digit picoseconds: for example, the streak camera or intensified CCD (ICCD) cameras are able to picture the motion of light.

One picosecond is equal to 1000 femtoseconds, or 1/1000 nanoseconds. Because the next SI unit is 1000 times larger, measurements of 10⁻¹¹ and 10⁻¹⁰ second are typically expressed as tens or hundreds of picoseconds. Some notable measurements in this range include:

• 1.0 picoseconds (1.0 ps) – cycle time for electromagnetic frequency 1 terahertz (THz) (1 x 10¹² hertz), an inverse unit. This corresponds to a wavelength of 0.3 mm, as can be calculated by multiplying 1 ps by the speed of light (approximately 3 x 10⁸ m/s) to determine the distance traveled. 1 THz is in the far infrared.
• 1 picosecond – time taken by light in vacuum to travel approximately 0.30 mm
• 1 picosecond – half-life of a bottom quark
• ~1 picosecond – lifetime of a single H
  ₃O⁺
  (hydronium) ion in water at 20 °C
• picoseconds to nanoseconds – phenomena observable by dielectric spectroscopy
• 1.2 picoseconds – switching time of the world's fastest transistor (845 GHz, as of 2006)
• 1.7 picoseconds - rotational correlation time of water
• 3.3 picoseconds (approximately) – time taken for light to travel 1 millimeter
• 10 picoseconds after the Big Bang – electromagnetism separates from the other fundamental forces
• 34 picoseconds - signal rise time (20% to 80%) of a SFP+ transmitter for 10 Gigabit Ethernet.
• 10–150 picoseconds – rotational correlation times of a molecule (184 g/mol) from hot to frozen water
• 100 picoseconds - Unit Interval of a 10 Gbps serial communication link, such as USB 3.1.
• 108.7827757 picoseconds – transition time between the two hyperfine levels of the ground state of the caesium-133 atom at absolute zero
• 330 picoseconds (approximately) – the time it takes a common 3.0 GHz computer CPU to complete a processing cycle