JWST is the formal successor to the Hubble Space Telescope (HST), and since its primary emphasis is on infrared observation, it is also a successor to the Spitzer Space Telescope.
JWST will far surpass both those telescopes, being able to see many more and much older stars and galaxies.
Observing in the infrared is a key technique for achieving this because of cosmological redshift and because it better penetrates obscuring dust and gas.
This allows observation of dimmer, cooler objects.
Since water vapor and carbon dioxide in the Earth's atmosphere strongly absorbs most infrared, ground-based infrared astronomy is limited to narrow wavelength ranges where the atmosphere absorbs less strongly.
Additionally, the atmosphere itself radiates in the infrared, often overwhelming light from the object being observed.
This makes a space telescope preferable for infrared observation.

The more distant an object is, the younger it appears: its light has taken longer to reach human observers.
Because the universe is expanding, as the light travels it becomes red-shifted, and objects at extreme distances are therefore easier to see if viewed in the infrared.
JWST's infrared capabilities are expected to let it see back in time to the first galaxies forming just a few hundred million years after the Big Bang.

Infrared radiation can pass more freely through regions of cosmic dust that scatter visible light.
Observations in infrared allow the study of objects and regions of space which would be obscured by gas and dust in the visible spectrum, such as the molecular clouds where stars are born, the circumstellar disks that give rise to planets, and the cores of active galaxies.

Relatively cool objects (temperatures less than several thousand degrees) emit their radiation primarily in the infrared, as described by Planck's law.
As a result, most objects that are cooler than stars are better studied in the infrared.
This includes the clouds of the interstellar medium, brown dwarfs, planets both in our own and other solar systems, comets and Kuiper belt objects that will be observed with the Mid-Infrared Instrument (MIRI) requiring an additional cryocooler.

Some of the missions in infrared astronomy that impacted JWST development were Spitzer and also the WMAP probe.
Spitzer showed the importance of mid-infrared, such as in its observing dust disks around stars.
Also, the WMAP probe showed the universe was "lit up" at redshift 17, further underscoring the importance of the mid-infrared.
Both these missions were launched in the early 2000s, in time to influence JWST development.
JWST is the formal successor to the Hubble Space Telescope (HST), and since its primary emphasis is on infrared observation, it is also a successor to the Spitzer Space Telescope. JWST will far surpass both those telescopes, being able to see many more and much older stars and galaxies. Observing in the infrared is a key technique for achieving this because of cosmological redshift and because it better penetrates obscuring dust and gas. This allows observation of dimmer, cooler objects. Since water vapor and carbon dioxide in the Earth's atmosphere strongly absorbs most infrared, ground-based infrared astronomy is limited to narrow wavelength ranges where the atmosphere absorbs less strongly. Additionally, the atmosphere itself radiates in the infrared, often overwhelming light from the object being observed. This makes a space telescope preferable for infrared observation.
The more distant an object is, the younger it appears: its light has taken longer to reach human observers. Because the universe is expanding, as the light travels it becomes red-shifted, and objects at extreme distances are therefore easier to see if viewed in the infrared. JWST's infrared capabilities are expected to let it see back in time to the first galaxies forming just a few hundred million years after the Big Bang.
Infrared radiation can pass more freely through regions of cosmic dust that scatter visible light. Observations in infrared allow the study of objects and regions of space which would be obscured by gas and dust in the visible spectrum, such as the molecular clouds where stars are born, the circumstellar disks that give rise to planets, and the cores of active galaxies.
Relatively cool objects (temperatures less than several thousand degrees) emit their radiation primarily in the infrared, as described by Planck's law. As a result, most objects that are cooler than stars are better studied in the infrared. This includes the clouds of the interstellar medium, brown dwarfs, planets both in our own and other solar systems, comets and Kuiper belt objects that will be observed with the Mid-Infrared Instrument (MIRI) requiring an additional cryocooler.
Some of the missions in infrared astronomy that impacted JWST development were Spitzer and also the WMAP probe. Spitzer showed the importance of mid-infrared, such as in its observing dust disks around stars. Also, the WMAP probe showed the universe was "lit up" at redshift 17, further underscoring the importance of the mid-infrared. Both these missions were launched in the early 2000s, in time to influence JWST development.
James Webb Space Telescope