A detailed study of infrared properties (reflectivity, conductivity, and dielectric response), emphasizing reproducible results from fully oxygenated

{YBa}_{2}

{Cu}_{3}

O_{7}

crystals (

T_{c}

≃93 K) and films, is presented. The extrapolated values of

σ_{1}

(ω) at low frequency are roughly consistent with the measured temperature-dependent dc resistivity. Although not well understood, this infrared conductivity can be interpreted in terms of a frequency-dependent scattering rate of ∼kT+ħω, with a low-frequency mass enhancement of roughly 2 to 4 associated with a carrier-spin related interaction. Infrared measurements polarized along the c axis suggest a conductivity anisotropy of roughly 40:1 near

T_{c}

in the normal state. In the superconducting state an energy scale of 2

Δ_{c}

≃3

{kT}_{c}

is suggested by c-axis polarized measurements, while a much larger characteristic energy of 2

Δ_{a - b}

≃8

{kT}_{c}

is evident in the (a-b)-plane conductivity. From the area missing from the conductivity up to this very large gap, a reasonable estimate (≃1700 Å) for the (a-b)-plane penetration depth is obtained. Evidence for non-BCS temperature dependence, strong pair breaking scattering, and possible fluctuation effects is discussed. A comparison to infrared data from

{Bi}_{2}

{Sr}_{2}

{CaCu}_{2}

O_{8 - y}

shows a similarly large energy scale, 2

Δ_{a - b}

≃8

{kT}_{c}

; for the cubic

{Ba}_{0.6}

K_{0.4}

{BiO}_{3}

superconductor a more conventional energy scale, 2Δ≃4

{kT}_{c}

is observed. The unusually large energy scale obtained from the (a-b)-plane measurements of the layered cuprates lies far beyond the range of previously studied superconducting energy gaps (2Δ≃3 to 5

{kT}_{c}

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