  We discuss extensions the CKKW-L and UMEPS tree-level matrix element and
parton shower merging approaches to next-to-leading order accuracy.
  The generalisation of CKKW-L is based on the NL3 scheme previously developed
for e+e- -annihilation, which is extended to also handle hadronic collisions by
a careful treatment of parton densities. NL3 is further augmented to allow for
more readily accessible NLO input.
  To allow for a more careful handling of merging scale dependencies we
introduce an extension of the UMEPS method. This approach, dubbed UNLOPS, does
not inherit problematic features of CKKW-L, and thus allows for a theoretically
more appealing definition of NLO merging.
  We have implemented both schemes in Pythia8, and present results for the
merging of W- and Higgs-production events, where the zero- and one-jet
contribution are corrected to next-to-leading order simultaneously, and higher
jet multiplicities are described by tree-level matrix elements. The
implementation of the procedure is completely general and can be used for
higher jet multiplicities and other processes, subject to the availability of
programs able to correctly generate the corresponding partonic states to
leading and next-to-leading order accuracy.
