  Solar flares and coronal mass ejections (CMEs) cause immediate and adverse
effects on the interplanetary space and geospace. The deeper understanding of
the mechanisms that produce them and the construction of efficient prediction
schemes are of paramount importance. The source regions of flares and CMEs
exhibit some common morphological characteristics associated with strongly
sheared magnetic polarity inversion lines, indicative of the complex magnetic
configurations that store huge amounts of free magnetic energy and helicity.
This knowledge is transformed into parameters that can help us distinguish
efficiently between quiet, flare-, and CME-productive active regions.
Nonetheless, flare and CME prediction still faces a number of challenges. The
magnetic field information is constrained at the photosphere and accessed only
from one vantage point of observation; the dynamic behavior of active regions
is still not fully incorporated into predictions; the stochasticity of flares
and CMEs renders their prediction probabilistic. To meet these challenges, new
properties have been put forward to describe different aspects of magnetic
energy storage mechanisms in active regions and offer the opportunity of
parametric studies for over an entire solar cycle. This inventory of predictors
now includes information from flow fields, transition region/coronal
spectroscopy, data-driven modeling of the coronal magnetic field, as well as
parameterizations of dynamic effects from time series. Further work towards
these directions may help alleviate the current limitations in observing the
magnetic field of higher atmospheric layers. This paper reviews these efforts
as well as the importance of transforming new knowledge into more efficient
predictors and including new types of data.
