All controlled airspace which is not Class A, B, C nor D is considered Class E airspace.
Three types of Class E airspace are depicted on VFR Sectional Charts: surface based, transitional areas, and federal airway.
Surface based Class E airspace is depicted by a magenta segmented line. On occasion it is included as an extension of Class D airspace. These extensions are used facilitate instrument approaches. If the extension is 2 NM or less, it is Class D airspace. If anyone extension is greater than 2 NM, then all extensions are Class E airspace. (A clearance is not necessary to transition though Class E extensions.)
Transitional areas are used to transition between the terminal and en route environment. The airspace begins at either 700 feet AGL (fading magenta band) or 1200 feet AGL (fading blue band).
Federal airways below 18,000 feet MSL are Class E airspace. These airways are also known as Vector airways and begin at 1200 feet AGL.
Surface based and transitional areas are individually tailored to fit the needs of the environment they serve.
Federal airways within Class E airspace begin at 1200 feet AGL and extend up to but not including 18,000 feet MSL. The width of a these airways is 8 NM. Airways exceeding 51 NM expand about 2 NM every 13 NM.
Unless designated at a lower altitude, Class E airspace begins at 14,500 feet MSL and continues up to but not including 18,000 feet MSL over the 48 contiguous States and Alaska.
A clearance is not required to enter Class E airspace.
A transponder is not required to operate within Class E airspace.
VFR visibility and cloud clearance requirements are the same as Class C and Class D when below 10,000 feet MSL. Above 10,000 feet MSL, the visibility requirement is extended to 5 SM and the cloud clearance requirement is extended to 1,000 feet below, 1,000 feet above, and 1 SM laterally from clouds.