Machine learning has achieved great successes in online advertising, recommender systems, financial market analysis, computer vision, computational linguistics, bioinformatics and many other fields. However, its success crucially relies on human machine learning experts, as human experts are involved to some extent, in all systems design stages. In fact, it is still common for humans to take critical decisions in aspects like: converting a real world problem into a machine learning one, data gathering, formatting and preprocessing, feature engineering, selecting or designing model architectures, hyper-parameter tuning, assessment of model performance, deploying online ML systems, among others.