  In recent years, the study of ladder materials has developed into a
well-established area of research within the general context of Strongly
Correlated Electrons. This effort has been triggered by an unusual
cross-fertilization between theory and experiments. In this paper, the main
experimental results obtained in the context of ladders are reviewed from the
perspective of a theorist. Emphasis is given to the many similarities between
the two-dimensional high-$\rm T_c$ cuprates and the two-leg ladder compounds,
including Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$ (14-24-41) which has a
superconducting phase at high pressure and a small hole density. Examples of
these similarities include regimes of linear resistivity vs temperature in
metallic ladders and a normal state with spin-gap or pseudogap characteristics.
Some controversial results in this context are also discussed. It is remarked
that the ladder 14-24-41 is the first superconducting copper-oxide material
with a non-square-lattice layered arrangement, and certainly much can be
learned from a careful analysis of this compound. A short summary of the main
theoretical developments in this field is also included, as well as a brief
description of the properties of non-copper-oxide ladders. Suggestions by the
author on possible experiments are described in the text. Overall, it is
concluded that the enormous experimental effort carried out on ladders has
already unveiled quite challenging and interesting physics that adds to the
rich behavior of electrons in transition-metal-oxides, and in addition
contributes to the understanding of the two-dimensional cuprates. However,
still considerable work needs to be carried out to fully understand the
interplay between charge and spin degrees of freedom in these materials.
