We analyze the spin- and charge-density oscillations near impurities in spi
n chains and quantum wires. These so-called Friedel oscillations give detai
led information about the impurity and also about the interactions in the s
ystem. The temperature dependence of these oscillations explicitly shows th
e renormalization of backscattering and conductivity, which we analyze for
a number of different impurity models. We are also able to analyze screenin
g effects in one dimension. The relation to the Kondo effect and experiment
al consequences are discussed.