I believe we're in the midst of a fundamental shift in the social sector. Over the last several months, nearly every leader I know in the field has started to ask the same types of questions: How can my organization create impact at a scale that actually approaches the size of the problem (i.e., create transformative scale)? When should I stop growing my direct-service operation and invest in other scale pathways? What can philanthropists do to support transformative scale? What kinds of "system change" and "field building" strategies really make a difference? What kinds of relationships between nonprofits, philanthropists, and government create the greatest potential for transformative scale?

When my Bridgespan colleague Abe Grindle and I wrote the article "Transformative Scale: The Future of Growing What Works" for the spring issue of Stanford Social Innovation Review, we hoped that it would spark sector-wide conversation and inspire further work on these critical questions. This series on scaling, presented in partnership with SSIR, represents the next step. Over the next eight weeks, 16 leaders from around the world will weigh in with their insights, struggles, and questions regarding the challenge of achieving impact at a scale that actually solves problems.

The social sector has been building up to this moment for some time. Over the past couple of decades, leaders have developed a growing catalog of programs and practices that have real evidence of effectiveness. And they've demonstrated the ability to successfully replicate these to multiple cities, states, even nations in some cases, reaching thousands or even millions of those in need. Despite all this progress, today even the most impressive programs and field-based practices rarely reach more than a tiny fraction of the population in need.

So we find ourselves at a crossroads. We have seen a burst of program innovation over the past two decades; we now need an equivalent burst of innovation in strategies for scaling.

The goal of this blog series is to continue to help spark sector-wide thinking and conversation around this challenge. Leaders from many different domains and positions in the sector will share their perspectives. Some will elaborate on pathways described in the SSIR article. Others will push into new territory, posing new questions and framing new perspectives on what it will take to achieve such scale. We also want to hear from you, particularly about practical insights into how to pursue pathways to transformative scale. Saying we need more "field building" or "systems change" begs for details: What are we really talking about and what does it really take?

I also invite you to join me next Tuesday, April 29, for a webinar conversation about transformative scale (registration is free). The webinar will provide a chance to hear from and engage directly with two contributors to the blog series—Gerald Chertavian, CEO of Year Up, and Susan Davis, cofounder, president, and CEO of BRAC USA , an independent grant-making affiliate of BRAC International. Chertavian and Davis represent two very different organizations, but both are grappling with this same issue.

In addition, an amazing group of leaders will contribute posts about different aspects of transformative scale—practical visionaries who are aiming for widespread, enduring change in the world. The series will feature:

Risa Lavizzo-Mourey, president and CEO of the Robert Wood Johnson Foundation, on creating a "culture" of health; Billy Shore, founder and CEO of Share Our Strength, on the transition to making real the No Child Hungry aspiration; Wendy Kopp, cofounder and CEO of Teach for All, on scaling an approach, not an organization, globally; Molly Melching, founder and executive director of Tostan, on listening to the community you serve; Charlie MacCormack, former CEO of Save the Children, on ways donor strategies impede achieving impact at scale; Rob Waldron, CEO of Curriculum Associates, on the key underpinning of any scale strategy—hiring great people; Mark Bonchek, founder and chief catalyst at thinkORBIT, on the importance of platforms versus products; Steve McCormick, former CEO of the Moore Foundation, on developing conservation's new paradigm; Rebecca Onie and Sonia Sarkar , cofounder, CEO, and chief of staff of Health Leads, on achieving impact at scale within the healthcare system; Kevin Hassey and Jordan Kassalow, CEO, and founder and cochairman, respectively, of Vision Spring, on testing multiple pathways to scale and sustainable business models; Michael Chu, Harvard Business School senior lecturer in the Social Enterprise Initiative, on systems change using commercial markets; and Nancy Lublin and Aria Finger, CEO and COO of Do Something, on the role of technology and demand-generation.

The aim of this blog series and webinar is to deliver a wealth of first-hand insights that will advance our collective understanding of transformative scale, and I hope it will engage others in the collective effort of finding pathways to profound change. Please join the conversation and post your own thoughts over the course of the series.

Jeff Bradach (@JeffBradach) is co-founder and managing partner of The Bridgespan Group. Before joining Bridgespan, he was on the faculty of the Harvard Business School.