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The typical neutral hydrogen column density is N(HI) approx 3.0 x 1018 cm-2 and the Doppler parameter is in the range 5 < b < 25 km s-11. Excited fine structure lines of CII* and SiII* are usually not seen, implying an electron density in the absorbing gas ne leq 10 cm-3. There is a wide range of ionization since N(CII) approx 1015 cm-2 and N(CIV) approx 1015 cm-2. From this we can deduce that the gas is probably photoionized by a flat-spectrum source (for example, the meta-galactic QSO flux), that the ionization parameter is Gamma = n(H) / n(gamma) = 6.5 x 103 and that a significant fraction of the gas is neutral. The heavy-elements are somewhat underabundant; Z approx 0.1 Zsun. Only crude limits can be placed on the sizes of the absorbing clouds. The line depths show that the clouds cover the QSO emission region which is estimated to have a size D approx 1019 cm. The Jeans length in the gas is estimated to be 2.4 x 1021 cm. The two lines of sight to the gravitationally lensed QSO, Q0957+551 (zem = 1.40), show the same C IV absorption redshifts at zem = 1.12, but the detailed absorption profiles are different (Boksenberg and Sargent 1983), implying individual cloud sizes of D < 2.7 x 1022 cm. On the other hand, this observation together with the observation (Shaver and Robertson 1983a; Boksenberg and Sargent 1983) of common absorption redshifts in the QSO pair UM680 / 681 whose separation is 1 arcmin or 300 kpc, implies that the absorption occurs in relatively small clouds which are embedded in much larger structures. The heavy-element redshift systems often exhibit velocity structure scales extending from 20 km s-1 (the lower limit that has been resolved) up to 600 km s-1. The value 150 km s-1 is typical. The number density of typical strong CIV redshift systems is dN / dz approx 1.5 at z = 2. As we shall see, there is no strong cosmological evolution in the density of absorbers.