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Nanomechanical testing methods originated in the 1980s with atomic force microscopy (AFM)-based indentation to probe the hardness and modulus of thin films. The subsequent development of standalone nanoindentation techniques resulted in an unprecedented, widespread expansion of the use of nanomechanical testing methods for a wide variety of materials—including metals and alloys, ceramics, biologic materials, and soft materials. Nanoindentation has also been uniquely applied to a wide variety of specimen configurations, including thin films, nanoparticles, composites, and surface layers such as tribologic coatings and ion-irradiated layers. The advent of site-specific focused ion beam (FIB) milling roughly 2 decades ago has enabled yet another rapid expansion of nanomechanical methods, specifically in situ mechanical tests conducted within a scanning electron microscope (SEM) using a depth-sensing holder. The method enables concurrent collection of load-displacement data and SEM resolution images or video of a specimen throughout the deformation process. In situ techniques offer transformative insight into deformation mechanisms and have thus been broadly adopted to test a wide range of materials in numerous configurations, including compression pillars, cantilevers or three-point bend beams, tensile bars, indentation, and creep. Within the past decade, development of depth-sensing transmission electron microscopic (TEM) in situ mechanical testing holders has further enhanced our ability to resolve and quantitatively understand nanomechanical phenomena. TEM in situ mechanical testing has been conducted in compression, tension, bending, and indentation modes to investigate a wide range of nanomechanical behaviors at the atomic through nano-scale, including dislocation slip, twinning, diffusionless phase transformations, bubble shearing, and irradiation effects. Advancements in computation since the late 1990s have developed in concert with the aforementioned experimental methods. Finite element and phase field models have been integrated with one another to introduce microstructural awareness to stress and strain distributions in a specimen during deformation. These models complement SEM in situ nanomechanical methods. Discrete dislocation dynamics (DDD) and molecular dynamics (MD) simulations, on the other hand, complement TEM in situ nanomechanical testing by providing a fundamental understanding of the interaction of dislocations with the material microstructure during deformation. All of these advancements in nanomechanical methods have required tight coupling of novel tools developed by researchers in industry, with applications refined at laboratories and in academia. In keeping with this trend, this JOM focus topic incorporates the latest developments from several industry leaders, with new methods developed by users across the research enterprise. This focus issue aims to further push the boundaries of nanomechanical methods to open new frontiers for nanomechanical testing, analysis, and understanding. Several papers within this focus issue are centered around evaluating parameters or behaviors that have historically been difficult to measure. For example, activation energies and enthalpies are hard to measure but are necessary to understand deformation mechanisms. Authors Ovri and Lilleodden have developed a nanoindentation-based method that uses the well-known Portevin-Le Chanterlier (PLC) effect to estimate activation enthalpies in an Al-Mg alloy. The new approach, thoroughly examined with respect to strain rate, indentation depth, and indenter geometry, derives values that are in good agreement with known Janelle P. Wharry is the JOM advisor for the Nanomechanical Materials Behavior Committee of the TMS Materials Processing & Manufacturing Division, and co-guest editor with Megan J. Cordill for the topic New Developments in Nanomechanical Methods in this issue. JOM, Vol. 71, No. 10, 2019